Plain English Meaning

It is the piece of database code that tells the navigation system two things at once: how to fly this part of the route and when this part is finished. Together those two pieces define one leg of the procedure.

Full Definition

A coded element within an RNAV procedure database that defines a single leg of a flight path by specifying both the type of path to be flown (such as a heading, course, or arc) and the event that ends that leg (such as reaching an altitude, a fix, or an intercept). Each leg in an RNAV departure, arrival, or approach is built from one of these path-terminator codes (for example, TF, CF, DF, VA, CA, RF), and the avionics use the field to compute and fly the leg automatically.