1. [n]  (genetics) abnormal complement of three X chromosomes in a female
2. [n]  the cardinal number that is the product of ten and three
3. [adj]  being ten more than twenty

XXX is a 3 letter word that starts with X.

/X-X-X/ A marker that attention is needed. Commonly used in program comments to indicate areas that are kluged or need to be. Some hackers liken "XXX" to the notional heavy-porn movie rating. Compare fixme.

[jargon file]