What is the meaning of possessive form?

Answer 1

In English nouns and pronouns have a form in which they show possession.

examples:

He is John. John owns a knife.

That is his knife.

That is John's knife.

In the examples above 'his' and 'John's' show possession of a knife.

Answer 2

The possessive form is a grammatical construction that indicates ownership or association. It is typically formed by adding an apostrophe and the letter "s" ('s) to a noun. For example, "Sarah's book" indicates that the book belongs to Sarah.