perineum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The portion of the body in the pelvis occupied by urogenital passages and the rectum, bounded in front by the pubic arch, in the back by the coccyx, and laterally by part of the hipbone.
2. n. The region between the scrotum and the anus in males, and between the posterior vulva junction and the anus in females.

Century Dictionary and Cyclopedia

1. n. The region of the body between the thighs, extending from the anus to the fourchette in the female, or to the scrotum in the male. In this, the usual surgical and obstetrical sense of the word, the term may include, in the female, all the deeper parts between the posterior wall of the vagina and the anterior wall of the rectum, or it may be more particularly applied to the superficial parts, the deeper parts receiving the name of perineal body.
2. n. The region included by the outlet of the pelvis, extending from the apex of the subpubic arch in front to the tip of the coccyx behind, and bounded laterally by the conjoined pubic and ischiatic rami, the tuberosities of the ischia, and the great sacrosciatic ligaments. It is occupied by the termination of the rectum, the urethra, the root of the penis in the male, or the termination of the vagina, the vulva, and the clitoris in the female, together with their muscles, fasciæ, vessels, and nerves. In this sense, the division in front of the anus is termed the urethral part, or the true perineum, and the posterior division, including the anus, is termed the anal part, ischiorectal region, or the false perineum.

Wiktionary

1. n. The region between the genital area and the anus in both sexes

GNU Webster's 1913

1. n. The region which is included within the outlet of the pelvis, and is traversed by the urinogenital canal and the rectum.

WordNet 3.0

1. n. the general region between the anus and the genital organs