peat moss • n. 1. a large absorbent moss (genus Sphagnum, family Sphagnaceae) that grows in dense masses on boggy ground, where the lower parts decay slowly to form peat deposits. Peat moss is widely used in horticulture, esp. for packing plants and for compost. 2. a lowland peat bog.

peat moss Decomposed organic matter (humus) obtained from disintegrated sphagnum moss (bog moss). The most widely obtainable source of humus, it is dug into soil and added to compost to retain moisture. Its continuing use poses an ecological threat to peat bogs.

peat moss The common name for a moss of the genus Sphagnum, common on wet peat.