A Clause must have -

• A clause must contain a subject and a verb.

Clause:
A clause is a part of a sentence. There are two main types: independent (main clauses), dependent (subordinate clauses).

Types of clauses:

Independent clauses:
A clause in a complex sentence that can stand alone as a complete sentence.
In other words,
An independent clause is a clause that can stand on its own as a distinct sentence.
Examples:
- I love eating cookies.
- My dog barks a lot.

Dependent clauses:
It needs an independent clause to finish or complete the sentence.
Ex. When I got home, I ate dinner.
Dependent clauses are sometimes known as subordinate clauses. Example: When I grow up

Source: Oxford Practice grammar and A passage to the English Language by S.M. Zakir Hussain.