From Teflpedia

The Genitive case, or simply genitive, or possessive case is a grammatical case found in English and other related languages.

In English, this is used to indicate possession. First, there are the possessive determiners, both dependent possessive determiners and independent possesive determiners are in the genitive case. Secondly, nouns other than pronouns, are inflected with the genitive 's suffix to show possession.

We use the genitive to talk about possession, relationship, physical features, etc. We use it to talk about a noun which “belongs” to a person, a country, organisation, etc.: John’s hair; Anne’s flat; the company's marketing strategy; Spain’s unemployment figures

  • we also use it to talk about something which is used by a person or animal: There are two birds’ nests in that tree; a child’s bicycle;
  • It can also be used for products from living animals: cow’s milk; lamb’s wool;
  • It is often used to say how long things last: three hours’ journey; twenty minutes’ delay;
  • It can indicate the origin of something in a proper name: Murphy's law;