in chemistry, the effective concentration of an ion or other solute for the purposes of chemical reactions and other mass action. Activity differs from concentration, because of the affinity of solutes for the solvent molecules around them in solution. To some extent this affinity restrains solutes from engaging in other interactions (such as with reactants). Because their affinities differ, so do solutes' activity coefficients. These describe the constant of proportionality between a solute's concentration and its activity in a given solvent (typically assumed to be water). Compare: fugacity.
in radioactivity, the number of disintegrations per second. It is measured in becquerel. For a given radioactive object, the activity is proportional to the number of atoms remaining. See: exponential decay.
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In grammar, the voice of a verb describes the relationship between the action (or state) that the verb expresses and the participants identified by its arguments (subject, object, etc.).
When the subject is the agent or actor of the verb, the verb is said to be in the active voice.
In other languages, such as Latin, the passive voice is simply marked on the verb by inflection: the passive voice uses different verb endings than the active voice.
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