Real Dictionary

flop
If something is a flop, it is completely unsuccessful.
verb: If something flops onto something else, it falls there heavily or untidily.
verb: If something flops, it is completely unsuccessful.
verb: If you flop into a chair, for example, you sit down suddenly and heavily because you are so tired.

flop in American English
to flap, strike, throw, or cause to drop noisily and clumsily
to move or flap around loosely or clumsily, usually with a thud or thuds
intransitive verb: to fall or plump down suddenly, esp. with noise; drop or turn with a sudden bump or thud
noun: an act of flopping
transitive verb: to drop with a sudden bump or thud

flop in British English
noun: the act of flopping
verb: to bend, fall, or collapse loosely or carelessly