One of the Ten Commandments states, “You shall not give false testimony against you neighbor”. What does that mean?

The commandment in question is found in Exodus 20:16. False testimony is lying about someone else. Usually it is a lie that will hurt someone’s reputation or defame his character. False testimony can also mean lying about what someone has done or not done. The United States justice system is based on truthful testimony.

A truthful witness gives honest testimony, but a false witness tells lies.

Proverbs 12:17

A false witness will not go unpunished, and he who pours out lies will not go free.

Proverbs 19:5