Extrasensory perception (more commonly abbreviated as ESP) is a term which is applied to the human ability to perform activities that utilize more advanced sensing abilities than are provided by the basic five senses. For centuries, many scientists believed that humans' ESP abilities were always going to be limited by the brain, however it had been proven that basic ESP abilities could allow someone to predict future events, start fires spontaneously and see through objects.
By the 23rd century, Starfleet recorded an officer's ESP ability as part of their routine medical and psychological evaluations. This was called the esper rating. (TOS episode & Star Trek 8 novelization: Where No Man Has Gone Before; TOS comic: "Star TreX"; TNG novel: The Valiant; TOS comics: "IDW Star Trek, Issue 1", "Issue 2")