A standard trigger is the same width along it's length.

A target trigger is wider at the point of finger contact, and gives the feeling of a lighter trigger pull because of it's greater finger contact area.

A standard hammer is also the same width along it's entire length.

A target hammer has a wider thumb spur and makes thumb cocking easier and faster.

Both of these were developed at the request of NRA target competion revolver shooters, and therefore are favored for use in the "bullseye" shooting sports.