The modifier letter apostrophe (ʼ) is a glyph.
In the International Phonetic Alphabet, it is used to express ejective consonants, such as / kʼ /, / tʼ /, etc.
It denotes a glottal stop (IPA /ʔ/) in orthographies of many languages, such as Nenets.
It is encoded at U+02BC ʼ MODIFIER LETTER APOSTROPHE (HTML ʼ).
In Unicode code charts it looks identical to the U+2019 ’ RIGHT SINGLE QUOTATION MARK, but (unlike the U+2019, which has the "Punctuation, Final quote" (Pf) General Category) it has the "Letter, modifier" (Lm) General Category.
Although the Unicode standard versions 1.0–2.1.9 considered this character as the "preferred character for apostrophe", then versions since 3.0.0, including the current one, consider the U+2019 ’ RIGHT SINGLE QUOTATION MARK as preferred one. There are reasoned objections to this decision (the main argument is that English apostrophe is a part of a word).
U+02BC ʼ MODIFIER LETTER APOSTROPHE plays the role of Ukrainian apostrophe in internationalized domain names.