Talk is cheap 意为「开空头支票;随便说说而已」。这个惯用语于 1800 年代开始使用至今,但确切起源不得而知。
1800 年代流行的成语中有几个是以talk is cheap 作开头,如talk is cheap but it takes money to buy a farm、talk is cheap but it takes money to buy whiskey、talk is cheap until you hire a lawyer 等等。

由于大家对上面各成语的后半段太熟悉了,因此往往略而不提。现今这些成语或惯用语都仅剩下前半段,亦即 talk is cheap,而后半段几乎已被忘得一干二净。
例句:

My boss keeps saying he’ll give me a promotion and raise, but talk is cheap. (我老板一直说他会给我升迁和加薪,但他乱开空头支票)
My husband has been promising me a new washing machine for three years now. Talk is cheap. (三年来我先生一直保证要给我买一台新的洗衣机。他随便说说而已)