Plain English Meaning
How sharply you are turning toward the line you want to be flying on. A small angle means you are easing onto it; a large angle means you are cutting across to it.
Full Definition
The angle, measured in degrees, between the heading the aircraft is flying and the desired course or navigational track it is attempting to join.
Context Anchor
Used during navigation when joining a selected route line, such as turning toward a course shown by a navigation instrument or correcting back toward the planned path.
Derivation
Intercept comes from the Latin intercipere, meaning to seize or catch between. Here, the pilot is catching the desired course by flying a heading that crosses it at a chosen angle.
Why Pilots Care
It determines how much heading change is needed to join the course smoothly without overshooting or excessive .