What is an apostrophe for possesion?

An apostrophe for possession is used to indicate that something belongs to someone or something. Typically, it is placed before the "s" for singular nouns (e.g., "the dog's leash") and after the "s" for plural nouns that already end in "s" (e.g., "the dogs' park"). For irregular plural nouns that do not end in "s," the apostrophe is placed before the "s" (e.g., "the children's toys"). This grammatical tool helps clarify ownership in writing.