grammatical error

17 LETTERS · STARTS WITH G

grammatical error is a valid 17-letter word worth 23 points in Scrabble and 28 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS

G2R1A1M3M3A1T1I1C3A1L1E1R1R1O1R1

2 + 1 + 1 + 3 + 3 + 1 + 1 + 1 + 3 + 1 + 1 + 0 + 1 + 1 + 1 + 1 + 1 =23 PTS

DOUBLE WORD → 46TRIPLE WORD → 69

MEANING

What does grammatical error mean?