From Diablo Wiki
"Gossips" are the gaming term for those casual comments NPCs make when they speak to you, without specifically talking about quests or missions. There are generally a pool of these gossips that they select from randomly, with some keyed specifically to given situations and others that they will only voice to a particular class.
You can see examples of gossips on the, where every piece of dialogue they utter in the entire game is sorted and listed.
Class Specific Gossips
Numerous examples of class-specific gossips can be seen in Diablo 2. For instance, Larzuk, the Act 5 NPC from Diablo 2, has a special affinity for Amazons, and in addition to his 8 general purpose, randomly-selected gossips, he has 2 other special gossips.
- I’ve heard that you Amazons excel at killing from a distance. From what I’ve seen, that’s the best way to deal with Hell’s minions. Are all of your kind so big?
- Why did you ever leave your beautiful islands to come to this frozen battleground? Perhaps if we both survive this, we’ll travel back there together.
Diablo 3 Gossips
Not enough is known yet about the Diablo 3 NPC dialogues to list any conversations or gossips, though they'll surely have them; the NPCs in virtually every RPG do.