Pon farr is a part of the Vulcan reproductive cycle occurring approximately once every seven years, during which a Vulcan must undergo the plak tow, or "blood fever" during which they lose all control of their emotions and are compelled to take a mate, or die. Pon farr affects both sexes, though the onset of pon farr in the female can sometimes be triggered by a telepathic link with a male. During pon farr, a Vulcan's biological functions increase from the norm and raise dangerously high in plak tow. If the Vulcan does not mate, the neurochemical balance may be fatal. During pon farr, a Vulcan is stripped of his or her logic and is flooded with uncontrollable emotions, often of an intensely sexual nature; he or she may become violent and unaware of his or her surroundings. Pon farr has also been known to be activated by interaction with pathogens. (TOS: "Amok Time," VOY: "Blood Fever," ENT: "Bounty")
Typically, a Vulcan will undergo this every seven years of their adult life during fertility. During this time, one would generate the urge to return to their homeworld to find a mate. However, there are other means of treating the pon farr, besides taking a mate.
On Stardate 50537.2, Ensign Vorik of the USS Voyager underwent his first pon farr - and due to Voyager's circumstances - Vorik would not be able to return to Vulcan to find a mate. He asked Chief Engineer B'Elanna Torres to be his mate (VOY: "Blood Fever") and when she refused, Vorik became filled with so much emotion that he assaulted Torres and began to initiate the pon farr via a mind meld on her. Through the telepathic link, Vorik was successful in infecting her with the condition.
Once briefed on the situation, Voyager's Security Chief Tuvok was instructed to help Vorik through means of extreme meditation - another means of treating the pon farr. Despite B'Elanna's new condition, she continued to refuse Vorik's demand that she be his mate. Lieutenant Torres expressed her desire to mate with fellow crewmate, Lieutenant Tom Paris, though he refused as he knew the condition was affecting her usual behavior.
Vorik then wished to initiate the Koon-ut-kal-if-fee - a "passion fight" - challenging Tom Paris as Paris himself began to give into B'Elanna's request to mate. B'Elanna then intervened and wished to fight for herself, eventually defeating Vorik and breaking the blood fever.