In set dances with more than one couple dancing, the couple doing the more complicated movement during any given portion of the dance. The role of active couple may pass from one couple to another. In many quadrilles, certain figures will have two active couples at any one time; in long set dances, quite often every other couple or every third couple is the active couple.

plural of active couple

(chemistry) A transitional structure, in an energetically excited state, that forms between the reactants of a chemical reaction and breaks down to form the products

The specific compound in a natural or man-made mixture that is responsible for the mixture's activity.

(astronomy) A galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy.

(chemistry, of a crystal or compound) Exhibiting optical activity.

(physics) a property caused by asymmetrical molecular or crystal structure that enables a compound or crystal to rotate the plane of incident polarized light

capable of lowering the surface tension of a liquid

Any activity done by an astronaut outside of a spacecraft etc; a spacewalk or moonwalk.

(physics, meteorology) The boundary between two different air masses, or a portion thereof, which produces appreciable cloudiness and precipitation and is usually accompanied by significant shifts in wind direction.