timothy or herd's-grass, perennial plant (Phleum pratense) of the family Gramineae (grass family), native to Europe and W Asia and one of the most widely cultivated hay grass of North America. Adaptable to cool, moist climates, where it is sometimes grown in mixtures (especially with red clover), it is a late grass—usually sown in the fall—and can be stored after cutting. It is not used for permanent pastures because it cannot survive continuous grazing. Timothy is classified in the division Magnoliophyta, class Liliopsida, order Cyperales, family Gramineae.