A gentleman is a man who comes from a family of high social standing.

If you say that a man is a gentleman, you mean he is polite and educated, and can be trusted.

You can address men as gentlemen, or refer politely to them as gentlemen.

A gentleman's agreement or a gentlemen's agreement is an informal agreement in which people trust one another to do what they have promised. The agreement is not written down and does not have any legal force.