A line of eclectic social science theories and research with its roots in a Soviet theory pioneered by Sergei Rubinstein in the 1930s, seeking to understand human activities as systemic and socially situated phenomena and to go beyond paradigms of reflexology and classical conditioning.

an activity started by the citizens themselves; social movement

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

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

Self-motion or the power of moving one's self or itself without foreign or external aid.

(law) An activity that is so dangerous that any person engaging in it will be held strictly liable for harm caused by engaging in the activity, no matter what precautions were taken to prevent harm; common examples include using explosives, radiation, and poisonous chemicals, and handling wild animals.

plural of beehive of activity

(psychology) Aimless, often self-comforting behavior displayed when in doubt, blocked or frustrated. / (more broadly) Something done needlessly when procrastinating.

The increase in rate of a chemical reaction caused by the presence of a catalyst. / An amount of catalyst, expressed as the increase of the rate of its reaction.

(embryology) A region of mesenchymal connective tissue that carries instructions which direct the developing limb bud to form along the anterior-posterior axis.