One of the many terms for the condition which makes someone androgen-insensitive. Basically, the body of whomever has this (and it can be either male or female) doesn't respond to testosterone. This theoretically exists in chromosomal females, but it has very little effect in the end, and so isn't ever recognized (though they would be more busty and have a lowered libido due to the lack of any influence of testosterone, and an FTM transsexual with this condition would be unable to take advantage of hormone-replacement therapy). In a chromosomal male, this results in him (or, more accurately, her) being an androgen insensitive XY.