- any coccoid rickettsia of the genus Chlamydia, parasitic in birds and mammals, including humans, and causing various infections, especially of the eyes, as trachoma, lungs, as psittacosis, and genitourinary tract, as urethritis or chlamydia.
- a widespread, often asymptomatic sexually transmitted disease caused by Chlamydia trachomatis, a major cause of nongonococcal urethritis in men and pelvic inflammatory disease and ectopic pregnancy in women.
- any Gram-negative bacteria of the genus Chlamydia, which are obligate intracellular parasites and are responsible for such diseases as trachoma, psittacosis, and some sexually transmitted diseases
