Definition of pipper in US English:

pipper

noun

United States Air Force
  • A gap at the centre of the reticle or cross-hairs on an optical gunsight. In later use also: the visible aiming point of a laser targeting system; the electronic representation of a weapons aiming point on the head-up display of a fighter aircraft.

Origin

1950s; earliest use found in Statesville (North Carolina) Record & Landmark. Probably from pip + -er.

Pronunciation

pipper

/ˈpɪpə/