What is the meaning of '?

An ASCII substitute for any of multiple characters with a similar shape:

1. ’ (apostrophe)
2. ‛ (leading apostrophe)
3. A quotation mark, in some languages: see ' '.
4. ˈ (primary stress)
5. ׳ (Hebrew geresh)
6. ꞌ (saltillo)

’ (apostrophe)

‛ (leading apostrophe)

A quotation mark, in some languages: see ' '.

ˈ (primary stress)

׳ (Hebrew geresh)

ꞌ (saltillo)

An ASCII substitute for a letter representing a glottal stop, or glottalization:

1. ' or ʼ
2. ꞌ (the saltillo, used in some languages of Mexico and Guatemala to represent either a glottal stop or a fricative sound).
3. ʻ (the Hawaiian okina).

' or ʼ

ꞌ (the saltillo, used in some languages of Mexico and Guatemala to represent either a glottal stop or a fricative sound).

ʻ (the Hawaiian okina).

Replaces one or more letters which have been removed from a written word, often but not always because they are not being pronounced.

Replaces letter(s) when two or more words are contracted into one word.

Similarly replaces one or more numbers which have been removed.

An ASCII substitute for the foot (length unit symbol).

An ASCII substitute for ′ (prime symbol).

An ASCII substitute for the symbol representing the minute, placed after the value of the seconds in a term to indicate minutes count.

Alternative form of ¯

A pointing mark in Anglican chant, which marks a place in the text where a barline occurs in the chant.

See ’

See -'.

sed to mark an initial a, e, or o in a multisyllabic Pinyin word, to prevent confusion (隔音符號／隔音符号 (géyīn fúhào))

Used to indicate omission of the a in la to form l'.

Used to indicate omission of the final -o of nominative singular nouns.

Indicates a syllable break in words, mostly as a result of consonant gradation.

Used to separate the inflectional ending from unadapted borrowings, chiefly when the borrowing ends in a silent consonant.

Used to signify omission or dropping of sounds.

1. Representing apocope found in poetic text.

   Representing apocope found in poetic text.

   Representing sounds elided as part of contractions.

   In some linguistic and grammatical sources, equivalent to ˣ.

   used to indicate truncation

   used after a word-final vowel, as a substitute for a grave or acute accent, especially in upper-case text

   Alternative form of ’

   put before the declension suffix of a foreign name, if the preceding letter is silent

   Replaces one or more letters which have been removed from a word.

   The apologetic apostrophe: inserted into a Scots word to give the appearance that it is a contraction of an English word.

   Source: wiktionary.org