(American football) A certain kind of play; see Wikipedia article for details.

(biology) Movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy.

(obsolete, rare, phrenology) The state or quality in which a person exhibits willingness to act rather than talk.

Making indirect use of solar energy by first converting it to another form (e.g. by using solar panels).

(grammar) A participle indicating an ongoing or completed action or state in the active voice, where a noun modified by the participle is taken to represent the agent of the action denoted by the verb.

Pronunciation spelling of acting.

(zoology) Any sea slug of the family Actaeonidae.

(grammar) A word that indicates an action, event or state.

(applied mathematics, insurance, finance) The discipline within applied mathematics dealing with risk assessment and the modelling of uncertainty; the rigorous application of mathematical and statistical methods to assess risk, in industries including insurance and finance.

a person or a group purchasing and using an equity stake in a publicly traded corporation to put public pressure on its management, with the goal of effecting a change