A clause can be performed as a/an:

Clauses can perform three distinct functions. They can operate as:

Noun clause: She completely understood everything he said.
Adjective clause: My friend who rides a motorcycle said it’s a great weekend to ride.
Adverb clause: She fixed the sink without facing difficulty.

Clause:
- It's an expression including a subject and predicate functioning as a part of a complex sentence.
- A clause is a part of a sentence. There are two main types: independent (main clauses), dependent (subordinate clauses).

Source: Oxford Practice Grammar.