yes, defamation is a communication about a person that hurts that person’s reputation. If the communication is spoken, then the defamation is called ‘slander’. If the communication is written, it is called ‘libel’.
If you defame someone, then you can be sued. And, the other person often doesn’t even have to prove that he/she suffered a financial loss from your remarks; a court will actually presume that he/she suffered losses and will make you pay!