variable error

14 LETTERS · STARTS WITH V

variable error is a valid 14-letter word worth 18 points in Scrabble and 21 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS

V4A1R1I1A1B3L1E1E1R1R1O1R1

4 + 1 + 1 + 1 + 1 + 3 + 1 + 1 + 0 + 1 + 1 + 1 + 1 + 1 =18 PTS

DOUBLE WORD → 36TRIPLE WORD → 54

MEANING

What does variable error mean?