flop1 past tense and past participle flopped, present participle flopping [intransitive]
1 [always + adverb/preposition]
to sit or lie down in a relaxed way, by letting all your weight fall heavily onto a chair etc:
He flopped down onto the bed.
I got home and flopped in front of the TV.
2 [always + adverb/preposition]
to hang or fall loosely, in an uncontrolled way:
His head flopped back pathetically.
if something such as a product, play, or idea flops, it is not successful because people do not like it