Possessive case is a case that exists in some languages used for possession. It is not the same as the genitive case, though the two have proximal meanings in many languages.

Alienable and Inalienable

There are many types of possession, but a common distinction is alienable versus inalienable possession. Alienability refers to the ability to dissociate something from its parent — in this case, a quality from its owner.

When something is inalienably possessed, it is usually an attribute: for example, John's big nose is inalienably possessed, because it cannot (without surgery) be removed from John — it's simply a quality he has. In contrast, 'my briefcase' is alienably possessed — it can be separated from me.

Many languages make this distinction in some way. Saying something like 'I have my dad's big nose' with the latter noun-phrase marked inalienable would imply some sort of genetic inheritance; marked alienable, it would imply that you had cut off your father's nose or somesuch and were actually in physical possession of it.

English does not have a grammatical facility to make such distinctions.

Inherent and Non-inherent

Another distinction, which is similar to alienable vs. inalienable possession, is inherent vs. non-inherent possession. In languages that mark this distinction, inherently possessed nouns, e.g., body parts, cannot be mentioned without also mentioning the possessor. So, you cannot say just 'a hand', but must also explicitly say whose hand it is. Several Papuan languages, for instance Mangga Buang, combine alienable/inalienable and inherent/non-inherent marking.

Possessable and Unpossessable

The Maasai language (and American Indian languages, at least according to urban legends) distinguish between the possessable and the unpossessable. Possessable things include farm animals, tools, houses, family members and money, while for instance wild animals, landscape features and weather phenomena cannot be possessed. Basically this means that, in such languages, saying 'my brother' is okay, but 'my land' would be grammatically incorrect. Instead, one would have to use a circumlocution such as 'the land that I own'.

Etymology

The term 'possessive case' is often used to refer to the "'s" morpheme, which is suffixed onto many nouns in English to denote 'possession by'. This categorization is arguably not strictly correct — some grammarians contend that this affix is actually a clitic. By descent, however, the English usage does stem from a case ending, Old English -es. See genitive case for details.