The grass family is defined by the following characteristics:
Habit: Herbs (or trees in the bamboos), fibrous roots
Stems: Hollow-pithed, round, swollen nodes
Leaves: Alternate, parallel leaf veins, with ligules
Inflorescence: grass spikelet, typically with 2 basal bracts (glumes) on a central axis and one to many florets, each consisting of a short lateral axis with 2 bracts (a lower, odd-veined lemma and an upper, 2-veined palea) and a flower
Flower: Typically bisexual, minute; perianth vestigial; stamens generally 3; stigmas generally 2, generally plumose
Fruit: Caryopsis (grain)
Link to Jepson key