What is the meaning of -'?

Possessive marker used on plurals that end with -s (or -es, etc).

Possessive marker sometimes used on singular names which end in s, indicating than an object belongs to the noun bearing the marker.

forms the possessive of words ending in s, x or z

Genitive suffix for words that end in a sibilant consonant. For other names, -s is used.

Used to form the genitive of nouns that already end in -s, -x or -z. For other nouns, -s is used.

Source: wiktionary.org

See also