A cousin in English kinship terminology is a relative with whom one shares a common grandparent or more distant ancestor, and who is not in one's own line of descent.

The term cousin never applies where there are other specific terms to describe relationships. These specific terms involve one's ancestors (mother, father, and all forms of grandparent) and their siblings (all forms of aunt and uncle), one's own descendants (child, grandchild, etc.), and one's own siblings (brother, sister) and their descendants (all forms of niece and nephew).

Cousin, the child of one's aunt or uncle or any relative who shares a common ancestor
Cousin Island, a small granitic island of the Seychelles
Cousin, cousine, a 1976 French language film which tells the story of cousins-by-marriage who have an affair
Cousin prime, a pair of prime numbers that differ by four
Cousin problems, two math questions in several complex variables, concerning the existence of meromorphic functions
Speci ...more

A relative

your uncle or aunt's son/daughter

brother or sister in an indirect relation. (e. g. son of your father's brother is your cousin brother

Cousin means who is related to you and who may be sons of your uncles or maternal uncles.

In colonial times, it most often meant nephew or niece. In the broader context, it could also mean any familial relationship, blood or otherwise,( except father, mother, brother, sister), or the contemporary meaning of a child of one's aunt or uncle. Modern usage includes qualifiers such as first, second, third, and once removed, twice removed, etc. First cousin is what most people commonly call their cousins, that is an aunt's or uncle's child.

brother and sister of your relatives

Not a direct relationship but an indirect relationship by virtue of ancestors of both father & mother.

son/daughter of sister or brother of father or mothert