Plain English Meaning
The pink-purple line on the GPS screen that shows the route the aircraft is supposed to follow. Stay on the line and you stay on course.
Full Definition
On a GPS or electronic flight display, the magenta-colored line that depicts the active flight plan course from the aircraft's current position to the next waypoint. The pilot navigates by keeping the aircraft tracking along this line.
Context Anchor
Seen on electronic flight displays when using the turn rate indicator during instrument flying.
Derivation
Magenta is a pinkish-purple named after the Battle of Magenta in northern Italy (1859), around the time the dye was first produced. chose magenta because it stands clearly against the typical dark background of an electronic without being confused with other colors used on the same screen (white, green, cyan, yellow).