Making out is a term of American origin, dating back to at least 1949, and is used variously to refer to kissing, petting, and necking, but may also refer to non-penetrative sex acts such as heavy petting. Snogging is a term with roughly the same meaning in British English and some related varieties of English, except in Hiberno-English (spoken in Ireland), where it is more commonly known as shifting.
Making out Wikipedia
The sexual connotations of the phrase "make out" appear to have developed in the 1930s and 1940s from the phrase's other meanings of "to succeed". Originally, it meant "to seduce" or "to have sexual intercourse with".
Studies indicate that at the beginning of the 20th century, premarital sex increased, and with it, petting behavior in the 1920s. The Continental experience at that time is amusingly illustrated by a letter that Sigmund Freud wrote to Sándor Ferenczi in 1931 playfully admonishing him to stop kissing his patients, in which Freud warned lest "a number of independent thinkers in matters of technique will say to themselves: Why stop at a kiss? Certainly one gets further when one adopts 'pawing' as well, which, after all, doesn't make a baby. And then bolder ones will come along who will go further, to peeping and showing – and soon we shall have accepted in the technique of analysis the whole repertoire of demi-viergerie and petting parties".
By the postwar period, necking and petting became accepted behavior in mainstream American culture, as long as the partners were dating, and became the subject of numerous jokes: 'He: "Darling, I'm groping for words." She: "You won't find them there." (N.Y. 1940)'.
Making out is usually considered an expression of affection or sexual attraction. An episode of making out is frequently referred to as a "make-out session" or simply "making out," depending on the speaker's vernacular. It covers a wide range of sexual behavior, and means different things to different age groups in different parts of the United States. It typically refers to kissing, including prolonged, passionate, open-mouth kissing (also known as French kissing), and intimate skin-to-skin contact. The term can also refer to other forms of foreplay such as heavy petting, which typically involves some genital stimulation, but usually not the direct act of penetrative sexual intercourse.
The perceived significance of making out may be affected by the age and relative sexual experience of the participants. Teenagers sometimes play party games in which making out is the main activity as an act of exploration. Games in this category include seven minutes in heaven and spin the bottle.
Teenagers may have had social gatherings in which making out was the predominant event. In the United States, these events were referred to as "make-out parties" and would sometimes be confined to a specific area, called the "make-out room". These make-out parties were generally not regarded as sex parties, though heavy petting may have been involved, depending on the group.