Plain English Meaning
Flying from where you are now onto the line you want to be tracking. You pick an angle that lets you cut across to the line, then turn to follow it once you reach it.
Full Definition
The procedure of flying an aircraft from its present position onto a desired course or track, using a chosen intercept angle to close the distance between the aircraft and the course line until the aircraft is established on it.
Context Anchor
Used during navigation when joining a planned route, an airway, or an approach path after starting from a position that is not already on it.