line of descent

NOUN
15 LETTERS · STARTS WITH L

line of descent is a valid 15-letter word worth 19 points in Scrabble and 23 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
L1I1N1E1O1F4D2E1S1C3E1N1T1
1 + 1 + 1 + 1 + 0 + 1 + 4 + 0 + 2 + 1 + 1 + 3 + 1 + 1 + 1 =19 PTS
DOUBLE WORD → 38TRIPLE WORD → 57
MEANING

What does line of descent mean?