ordered series

NOUN
14 LETTERS · STARTS WITH O

ordered series is a valid 14-letter word worth 15 points in Scrabble and 15 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
O1R1D2E1R1E1D2S1E1R1I1E1S1
1 + 1 + 2 + 1 + 1 + 1 + 2 + 0 + 1 + 1 + 1 + 1 + 1 + 1 =15 PTS
DOUBLE WORD → 30TRIPLE WORD → 45
MEANING

What does ordered series mean?