This Slang page is designed to explain what the meaning of flop is. The slang word / phrase / acronym flop means . Online Slang Dictionary. A list of slang. Ref- *whistle* Offensive foul on the Knicks! Lebron- Yo, thanks ref, i thought i broke something on that play. Tyson Chandler- Flop! I barely touched him!!. Define flop: to fall, lie, or sit down in a sudden, awkward, or relaxed way — flop in a sentence. He fell with a flop on the bed. It was a catastrophic box office flop and savaged by critics. View American English definition of flop. The Longest Journey E. Are you kidding me? His hair flopped over his left eye. Many of the big internet companies in the US have flopped badly in China.