is (v.) Look up is at Dictionary.com
third person singular present of be, Old English is, from Germanic stem *es- (cognates: Old High German, German, Gothic ist, Old Norse es, er), from PIE *es-ti- (cognates: Sanskrit asti, Greek esti, Latin est, Lithuanian esti, Old Church Slavonic jesti), from PIE root *es- "to be." Old English lost the final -t-. See be. Until 1500s, pronounced to rhyme with kiss. Phrase it is what it is, indicating resigned acceptance of an unpleasant but inevitable situation or circumstance about which nothing positive really can be said, is attested by 2001.