What is "quitch grass"

Quitch grass \Quitch" grass`\ (kw[i^]ch" gr[.a]s`). [Properly quick grass, being probably so called from its vigorous growth, or from its tenacity of life. See Quick, and cf. Couch grass.] (Bot.) A perennial grass ( Agropyrum repens) having long running rootstalks, by which it spreads rapidly and pertinaciously, and so becomes a troublesome weed. Also called couch grass, quack grass, quick grass, twitch grass. See Illustration in Appendix.