Caryopsis

In botany, a caryopsis (pl. caryopses) is a type of simple fruit—one that is monocarpellate (formed from a single carpel) and indehiscent (not opening at maturity) ^[1] and resembles an achene, except that in a caryopsis the pericarp is fused with the thin seed coat.

The caryopsis is popularly called a grain and is the fruit typical of the family Poaceae (or Gramineae), which includes wheat, rice, and maize.^[2]

The term grain is also used in a more general sense as synonymous with cereal (as in "cereal grains", which include some non-Poaceae). Considering that the fruit wall and the seed are intimately fused into a single unit, and the caryopsis or grain is a dry fruit, little concern is given to technically separating the terms fruit and seed in these plant structures. In many grains, the "hulls" to be separated before processing are flower bracts.