Anorgasmia is a form of sexual dysfunction (specifically orgasmic dysfunction) - sometimes classified as a psychiatric disorder - where the patient cannot achieve orgasm, even with "adequate" stimulation. Although it is reasonably uncommon overall, it is far more common in females than in males.
Primary anorgasmia is when the patient has never had an orgasm before and secondary anorgasmia is when the patient has had orgasms in the past but cannot have them now.
The most common causes of anorgasmia are social and psychological but medical problems should be considered. Some anti-depressant drugs are known to cause anorgasmia.