Few linguists have endeavored to clearly define what constitutes slang. Attempting to remedy this, Bethany K. Dumas and Jonathan Lighter argue that an expression should be considered "true slang" if it meets at least two of the following criteria:
It lowers, if temporarily, "the dignity of formal or serious speech or writing"; in other words, it is likely to be considered in those contexts a "glaring misuse of register".
Its use implies that the user is familiar with whatever is referred to, or with a group of people who are familiar with it and use the term.
"It's a taboo term in ordinary discourse with people of a higher social status or greater responsibility."
It replaces "a well-known conventional synonym." This is done primarily to avoid discomfort caused by the conventional synonym or discomfort or annoyance caused by having to elaborate further.
Michael Adams remarks that, "[Slang] is liminal language... it is often impossible to tell, even in context, which interests and motives it serves... slang is on the edge." Slang dictionaries, collecting thousands of slang entries, offer a broad, empirical window into the motivating forces behind slang".
While many forms of language may be considered "sub-standard", slang remains distinct from colloquial and jargon terms because of its specific social contexts. While considered inappropriate in formal writing, colloquial terms are typically considered acceptable in speech across a wide range of contexts, while slang tends to be considered unacceptable in many contexts. Jargon refers to language used by personnel in a particular field, or language used to represent specific terms within a field to those with a particular interest. Although jargon and slang can both be used to exclude non–group members from the conversation, the intention of jargon is to optimize conversation using terms that imply technical understanding. On the other hand, slang tends to emphasize social and contextual understanding.
While colloquialisms and jargon may seem like slang because they reference a particular group, they do not fit the same definition, because they do not represent a particular effort to replace standard language. Colloquialisms are considered more standard than slang, and jargon is often created to talk about aspects of a particular field that are not accounted for in the standard lexicon.
It is often difficult to differentiate slang from colloquialisms and even more standard language, because slang generally becomes accepted into the standard lexicon over time. Words such as "spurious" and "strenuous" were once slang, though they are now accepted as standard, even high register words. The literature on slang even discusses mainstream acknowledgment of a slang term as changing its status as true slang, because it has been accepted by the media and is thus no longer the special insider speech of a particular group. Nevertheless, a general test for whether a word is a slang word or not is whether it would be acceptable in an academic or legal setting, as both are arenas in which standard language is considered necessary and/or whether the term has been entered in the Oxford English Dictionary, which some scholars claim changes its status as slang.
It is often difficult to collect etymologies for slang terms, largely because slang is a phenomenon of speech, rather than written language and etymologies which are typically traced via corpus.
Eric Partridge, cited as the first to report on the phenomenon of slang in a systematic and linguistic way, postulated that a term would likely be in circulation for a decade before it would be written down. Nevertheless, it seems that slang generally forms via deviation from a standard form. This "spawning" of slang occurs in much the same way that any general semantic change might occur. The difference here is that the slang term's new meaning takes on a specific social significance having to do with the group the term indexes.
Coleman also suggests that slang is differentiated within more general semantic change in that it typically has to do with a certain degree of “playfulness". The development of slang is considered to be a largely “spontaneous, lively, and creative” speech process.
Still, while a great deal of slang takes off, even becoming accepted into the standard lexicon, much slang dies out, sometimes only referencing a group. An example of this is the term "groovy" which is a relic of 1960's and 70's American "hippy" slang. Nevertheless, for a slang term to become a slang term, people must use it, at some point in time, as a way to flout standard language. Additionally, slang terms may be borrowed between groups, such as the term "gig" which was originally coined by jazz musicians in the 1930s and then borrowed into the same hippy slang of the 1960s. 'The word "groovy" has remained a part of subculture lexicon since its popularization. It is still in common use today by a significant population. The word "gig" to refer to a performance very likely originated well before the 1930s, and remained a common term throughout the 1940s and 1950s before becoming a vaguely associated with the "hippy slang of the 1960s". The word "gig" is now a widely accepted synonym for a concert, recital, or performance of any type. "Hippy" is more commonly spelled "hippie".
Generally, slang terms undergo the same processes of semantic change that words in the regular lexicon do.
Slang is usually associated with a particular group and plays a role in constructing our identities. While slang outlines social space, attitudes about slang partly construct group identity and identify individuals as members of groups. Therefore, using the slang of a particular group will associate an individual with that group. Using Silverstein's notion of different orders of indexicality, it can be said that a slang term can be a second-order index to this particular group. Employing a slang term, however, can also give an individual the qualities associated with the term's group of origin, whether or not the individual is actually trying to identify as a member of the group. This allocation of qualities based on abstract group association is known as third-order indexicality.
As outlined by Elisa Mattiello in her book, a slang term can take on various levels of identification. Giving the examples of the terms "foxy" and "shagadelic", Mattiello explains that neither term makes sense given a standard interpretation of English:"foxy", although clearly a "denominal adjective" from its -y suffix, does not make sense semantically, as it is a synonym with sexy and has nothing to do with foxes;
"shagadelic" is a combination of a slang term with a slang suffix and therefore is considered an "extra-grammatical" creation.
Nevertheless, Matiello concludes that those agents who identify themselves as "young men" have "genuinely coined" these terms and choose to use them over "canonical" terms —like beautiful or sexy—because of the indexicalized social identifications the former convey.
In terms of first and second order indexicality, the usage of speaker-oriented terms by male adolescents indicated their membership to their age group, to reinforce connection to their peer group, and to exclude outsiders.
In terms of higher order indexicality, anyone using these terms may desire to appear fresher, undoubtedly more playful, faddish, and colourful than someone who employs the standard English term "beautiful". This appearance relies heavily on the hearer's third-order understanding of the term's associated social nuances and presupposed use-cases.
Often, distinct subcultures will create slang that members will use in order to associate themselves with the group, or to delineate outsiders.
Slang terms are often known only within a clique or ingroup. For example, Leet ("Leetspeak" or "1337") was originally popular only among certain Internet subcultures, such as software crackers and online video gamers. During the 1990s, and into the early 21st century, however, Leet became increasingly more commonplace on the Internet, and it has spread outside Internet-based communication and into spoken languages. Other types of slang include SMS language used on mobile phones, and "chatspeak", (e.g., "LOL", an acronym meaning "laughing out loud" or "laugh out loud" or ROFL, "rolling on the floor laughing"), which are widely used in instant messaging on the Internet.
As subcultures are also often forms of counterculture and counterculture itself can be defined as going against a standard, it follows that slang has come to be associated with counterculture.
Slang is often taken from social media as a sign of social awareness and shared knowledge of popular culture. This particular branch of slang has become more prevalent since the early 2000s as a result of the rise in popularity of social networking services, including Facebook, Twitter, and Instagram. This has created new vocabularies associated with each new social media venue, such as the use of the term “friending” on Facebook, which is a verbification of “friend” used to describe the process of adding a new person to one's list of friends on the website, despite the existence of an analogous term “befriend“. This term is much older than Facebook, but has only recently entered the popular lexicon. Unlike most slang, social media slang is often not spoken aloud in conversation, but rather written, though it is still not viewed as acceptable in a formal setting. Other examples of the slang found in social media include a general trend toward shortened words or acronyms. These are especially associated with services such as Twitter, which has a 140 character limit for each message and therefore requires a briefer, more condensed manner of communication. This includes the use of hashtags which explicitly state the main content of a message or image, such as #food or #photography.
In its earliest attested use (1756), the word slang referred to the vocabulary of "low or disreputable" people. By the early nineteenth century, it was no longer exclusively associated with disreputable people, but continued to be applied to language use below the level of standard educated speech. The origin of the word is uncertain, although it appears to be connected with thieves' cant. A Scandinavian origin has been proposed (compare, for example, Norwegian slengenavn, which means "nickname"), but is discounted by the Oxford English Dictionary based on "date and early associations". Jonathan Green however agrees with the possibility of a Scandinavian origin, suggesting the same root as that of sling, which means "to throw", and noting that slang is a thrown language - a quick, honest way to make your point.