“卖力”，或“卖力气”，字面意思是“sell one's strength”，形容一个人尽力地付出自己的劳动（exert all one's strength），可以翻译为“do one's very best”或“exert oneself to the utmost”。

例句：

他可能有点慢，但却是个肯卖力气的人。

He may be slow, but he always does his best.

他学法语很卖力。

He works hard at his French study.