I know flams and drags are grace note patterns (like the acciaccatura on piano) on drum kit, but is it different to 'flam drag?' or is just a matter of wording?
a grace note followed by an accent
two quick grace notes followed by an accent
The amount of space between the two notes in a drag is somewhat subjective. Depending on whether you are a drum-set player (probably diddle) or a rudimental snare player (a buzz). This explains more exactly:
To answer your question: a flam drag is a mixture of both.