You have studied other human beings, giving you inside knowledge of their emotional reaction to you. You will see the reaction level of the person you are talking to when involved in an indepth conversation.
”— Fallout 2 description
Empathy is a perk in Fallout.
The perk displays the effect dialogue options have on the NPC's reaction level. The perk is useless, as reaction has a trivial effect on gameplay, the effect can be easily inferred from the dialogue, and there's no point in making NPCs feel particularly happy.