Plain English Meaning
It is the south-pointing side of a localizer beam, used in a coded flight procedure to guide the aircraft along that beam to a specific point.
Full Definition
An RNAV path and terminator leg type (CF, or Course to Fix) that follows a localizer course on its south-facing alignment, used in coded instrument procedure data to guide the aircraft along the localizer signal toward a defined fix. It is the localizer course flown when the procedure is oriented to the south, as opposed to the north course of the same localizer.
Context Anchor
Seen in instrument procedure descriptions and path-leg coding when a procedure tells the aircraft or pilot to intercept or follow a specific localizer course.