engaged in action; characterized by energetic work, participation, etc.; busy

an active life.

being in a state of existence, progress, or motion

active hostilities.

involving physical effort and action

active sports.

having the power of quick motion; nimble

active as a gazelle.

characterized by action, motion, volume, use, participation, etc.

an active market in wheat; an active list of subscribers.

causing activity or change; capable of exerting influence ( opposed to passive )

active treason.

effective ( opposed to inert )

active ingredients.

Grammar . noting or pertaining to a voice of verbal inflection in which typically the subject of the sentence is represented as performing the action expressed by the verb ( opposed to passive )

Writes in He writes a letter every day is an active verb form.

requiring or giving rise to action; practical

an active course.

(of a volcano) in eruption.

Accounting . profitable; busy

active accounts.

requiring personal effort or attention; not automatic

an active alarm system.

interest-bearing

active paper.

Medicine/Medical . acting quickly; producing immediate effects

active remedies.

Sociology . (of a crowd) engaging in purposeful activity, often of a militant nature. Compare expressive ( def. 4 ) .

Aerospace . able to transmit signals

an active communications satellite.

Electronics . (of a device or system) acting as a source of electrical energy, as a generator, or capable of amplifying or converting voltages or currents, as a transistor or diode.

(of a solar heating system) accumulating and distributing solar heat by mechanical means.

Military . serving on active duty.

Grammar .

the active voice.

a form or construction in the active voice.

an active person, member, subscriber, etc.

The circular was mailed only to the actives on our list.

Informal . something showing considerable action or activity

On the stock market there was heavy trading in the actives.