A subordinate clause, also known as a dependent clause, is a group of words that includes a subject and a verb but does not express a complete thought. It cannot stand alone as a sentence and is dependent on a main (independent) clause to provide context and meaning. Subordinate clauses often begin with subordinating conjunctions like "because," "although," "if," "when," "while," "since," and "unless."
For example, in the sentence "Although it was raining, we decided to go for a walk," "Although it was raining" is a subordinate clause. It provides additional information but cannot stand alone as a complete sentence. The main clause "we decided to go for a walk" expresses a complete thought.