Lines in a drama in which a character reveals his or her thoughts to the audience, but not to the other characters, by speaking as if to himself or herself.
"I'll answer by doing the Highland fling or the sailor's hornpipe; and you — well, let me see — oh, I've got it — you can do Hamlet's soliloquy."
"Hamlet's soliloquy, you know; the most celebrated thing in Shakespeare. Ah, it's sublime, sublime! Always fetches the house."
From Mark Twain's Adventures of Huckleberry Finn.