Opposite of abiotic (environmental) factors. Living organisms (plants, insects, bacteria, animals) in an ecosystem interact with (other) plants and have an influence on the growth and development of those plants. The interaction can include such things as competition (for water, nutrients), parasitism (by aphids), symbiosis (by mycorrhiza).
Synonym: biotic components
OT: biotic factors ↔ abiotic factors
BT: environmental factors