Meaning

noun the concentration of attention or energy on something

noun maximum clarity or distinctness of an image rendered by an optical system

noun maximum clarity or distinctness of an idea

originBorrowed from Latin focus (“hearth, fireplace”); see there for more. Related to fuel. Kepler introduced the term into mathematics and the sciences in describing elliptical orbits of planets (quote from Nicholas Mee) : "One of the interesting properties of an ellipse is that if there were a light bulb at one focus, then all the light that it emits would reflect off the ellipse and converge at the…

Etymology from Wiktionary, CC BY-SA 3.0