Gossip

"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 Diablo 2 NPC pages, 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 he only voices to Amazons.

• 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.