Arcsecond
A second of arc or arcsecond is a unit of angular measurement which comprises one-sixtieth of an arcminute, or, put another way, 1/3600 of a degree of arc. The symbol for marking the arcsecond is the double prime (″) (U+2033, ″). One arcsecond would be 1″ (or 1").It can be abbreviated as arcsec, but should then not be confused with the inverse trigonometric function arc secant, which has the same abbreviation.
See also the definition for parsec, an astronomical distance unit which is in part defined from this angular measurement. In fact, it may be one of the most common usages of an arcsecond.