Definitions of activity:

• noun:   any specific activity

  Example: "They avoided all recreational activity"

• noun:   (chemistry) the capacity of a substance to take part in a chemical reaction

  Example: "Catalytic activity"

• noun:   the trait of being active; moving or acting rapidly and energetically

  Example: "The level of activity declines with age"

• noun:   the state of being active

  Example: "His sphere of activity"

• noun:   an organic process that takes place in the body

  Example: "Respiratory activity"

• noun:   a process existing in or produced by nature (rather than by the intent of human beings)

  Example: "Volcanic activity"