A collective noun is a noun used for a group of people or things. The noun 'group' is a generic collective noun which can be used for anything. The only standard collective noun use of the noun 'group' is a group of guinea pigs.
The noun group is a singular, common noun. The noun group can be used as a concrete or an abstract noun; the noun group can be used as a collective noun. Concrete, collective: a group of people, a group of furniture. Abstract, collective: a group of opinions, a group of principles.
The term is a collective noun. For example, the collective noun for a group of cows is a herd. The collective noun for a group of lions is called a pride. The collective noun for a group of geese is called a gaggle.
There is no standard collective noun for a group of hikers, however, a collective noun is an informal part of language. Any noun that is suitable can function as a collective noun, such as a group of hikers.