redtop Play nounA perennial grass (Agrostis gigantea) with reddish spikelets, native to Eurasia and widely cultivated for forage.nounA kind of bent-grass, Agrostis vulgaris (A. alba, var. vulgaris).nounA kind of grass (Agrostis vulgaris) highly valued in the United States for pasturage and hay for cattle; — called also English grass, and in some localities herd’s grass. See Illustration in Appendix. The tall redtop is Triodia seslerioides.nounA kind of grass (Agrostis vulgaris) highly valued in the United States for pasturage and hay for cattle.nounSpecies of the genus Agrostis, the bentgrasses.