To make sure you do not gossip, ask yourself three questions regarding what you want to say. The answer has to be "yes" to all three questions.
1. Is it true?
2. Is it charitable?
3. Does the person I want to tell it to need to know?
Remember the sin of detraction is when you say something that is true, but it is not charitable to repeat as it may ruin the subjects reputation as they may have repented of what they had done or been ignorant.