interchangeability

NOUN
18 LETTERS · 7 SYLLABLES · STARTS WITH I

interchangeability is a valid 18-letter word worth 29 points in Scrabble and 33 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
I1N1T1E1R1C3H4A1N1G2E1A1B3I1L1I1T1Y4
1 + 1 + 1 + 1 + 1 + 3 + 4 + 1 + 1 + 2 + 1 + 1 + 3 + 1 + 1 + 1 + 1 + 4 =29 PTS
DOUBLE WORD → 58TRIPLE WORD → 87
MEANING

What does interchangeability mean?