Anything I say about another person is gossip if it will in any way influence the listener's feelings about the person I'm talking about. This can be a true statement, or a false one. It could be juicy, or dry and factual. For example, even if every one of these comments were true, they could rightly be considered gossip:
'J. is having an affair.' (J., you could tell anyone you wanted this about yourself IF it were true, but that person, turning around and telling someone else, would be gossiping.)
'Sam always arrives late.' (Allowable: Sam called to let us know he'd get here in half an hour, so let's go ahead and eat!)
'Susie thinks she's hot stuff.' (No matter how obvious this may seem, it's not our business what Susie thinks. If we have that opinion, there's no harm keeping it to ourselves. Then others get to form their own opinions of Susie. Some might think she's adorable and humble.)
Even positive information can be interpreted as gossip if it's designed to influence others' feelings. Comments can cause envy or other negative feelings, or not be at all what another person sees or experiences about another person.
'My son gets straight A's on every report card.' (Save this for times when all parents present are bragging up their kids, and preferably not in the child's presence.)
'Bob is the nicest man you could ever hope to meet.' (More accurate: I have really enjoyed knowing Bob. He's always been polite and kind TO ME.)
'You can always trust my brother.' (More accurate: I always trust my brother.)
There are some religious traditions that discourage talking about anyone outside their presence if it includes any opinion of that person or his actions. This is very hard to do, but we can work to keep our observations as objective and non-controversial as possible. Even that's hard to do. I've been working at it for decades, and I know I still slip up.