Wiktionary
n. (context grammar English) a sentence that contains an independent clause as well as one or more dependent clauses, such as a relative clause, an adverbial clause, or a noun clause.(examples-right width=30% examples=This not the droid that you are looking for.
The dog came when she was called.
He said that he would do it tomorrow.)
WordNet
n. a sentence composed of at least one main clause and one subordinate clause
Usage examples of "complex sentence".
They had read nothing of the ledger except the boxed mottos and an occasional phrase or two which, mostly owing to Harold's convoluted style (the compound-complex sentence seemed to have been invented with Harold Lauder in mind), meant little or nothing.
Whisper a complex sentence to one, who then whispers the same message to the next, and so on.
A cat has claws at the end of its paws, and a complex sentence has a pause at the end of its clause.