pair annihilation

17 LETTERS · STARTS WITH P

pair annihilation is a valid 17-letter word worth 21 points in Scrabble and 25 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS

P3A1I1R1A1N1N1I1H4I1L1A1T1I1O1N1

3 + 1 + 1 + 1 + 0 + 1 + 1 + 1 + 1 + 4 + 1 + 1 + 1 + 1 + 1 + 1 + 1 =21 PTS

DOUBLE WORD → 42TRIPLE WORD → 63

MEANING

What does pair annihilation mean?