Complex sentence

A complex sentence is a sentence that has at least one dependent clause—for example:

So it isn’t surprising that his song about mass-murderer Charles Whitman is gloriously irreverent and wildly offensive. [AV Club]

Independent clause: So it isn’t surprising

Dependent clause: that his song about mass-murderer Charles Whitman is gloriously irreverent and wildly offensive

It begins when young sisters Scarlett and Rosie March are attacked in their home by a Fenris . . . [Novel Novice]

Independent clause: It begins

Dependent clause: when young sisters Scarlett and Rosie March are attacked in their home by a Fenris

The fat man seated in front of Patricia Marx, I learn, has “a bad case of sleep apnea.” [The Paris Review Blog]

Independent clause: The fat man . . . has “a bad case of sleep apnea.”

Dependent clauses: 1) [who is] seated in front of Patricia Marx; 2) I learn

A complex sentence that is also a compound sentence (one with two or more independent clauses) becomes a complex-compound sentence.