What is the grammatical name and function of this sentence when he came back?

The sentence "when he came back" is a dependent clause functioning as an adverbial clause of time.

Here's why:

* Dependent Clause: It contains a subject ("he") and a verb ("came") but cannot stand alone as a complete sentence. It needs an independent clause to be complete.

* Adverbial Clause: It modifies the main clause of the sentence by telling us when something happened.

* Time: The clause specifies the time at which the action of the main clause occurred.

Example:

* When he came back, he was tired.

In this example, "when he came back" tells us when he was tired. Without this clause, the sentence would be incomplete and lack context.