-'s
suffix
forming the possessive singular of nouns and some pronouns
man's; one's
forming the possessive plural of nouns whose plurals do not end in -s
children's
forming the plural of numbers, letters, or symbols
20's; p's and q's
informal
contraction of is or has
he's here; John's coming; it's gone
informal
contraction of us with let
let's
informal
contraction of does in some questions
where's he live?; what's he do?
Word Origin for -'s
senses 1, 2: assimilated contraction from Middle English
-es, from Old English, masculine and neuter genitive singular; sense 3, equivalent to
-s
1