(chiefly countable) A conifer of the genus Abies. / (chiefly countable) Any pinaceous conifer of related genera, especially a Douglas fir (Pseudotsuga) or a Scots pine (Pinus sylvestris).

(signal processing, of a filter) Initialism of finite impulse response; that has impulse response (or response to any finite length input) of finite duration.

(aviation) Initialism of flight information region; a specified region of airspace in which a flight information service (FIS) and an alerting service (ALRS) are provided

plural of fir

plural of firring

(architecture) Alternative form of furring

plural of FIR

A North American species of fir tree (Abies balsamea).

A European silver fir (Abies alba), native to Europe. / A Pacific silver fir (Abies amabilis), native to western North America / A Pindrow fir (Abies pindrow), native to Asia

The conical fruit of a fir tree.