index error

11 LETTERS · STARTS WITH I

index error is a valid 11-letter word worth 18 points in Scrabble and 19 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS

I1N1D2E1X8E1R1R1O1R1

1 + 1 + 2 + 1 + 8 + 0 + 1 + 1 + 1 + 1 + 1 =18 PTS

DOUBLE WORD → 36TRIPLE WORD → 54

MEANING

What does index error mean?