The phrase "spontaneous activity" refers to actions or behaviors that happen without any planning or external influence. It means doing something out of your own initiative or without thinking too much about it in that moment. Full definition
This is the exact reason why you as a parent must plan several, spontaneous activities which your baby can enjoy. (shrewdmommy.com)
It includes energy needed to obtain, digest, and absorb food in amounts to maintain body weight, as well as energy for spontaneous activity. (merckvetmanual.com)
Divine justice, on the other hand, is not abstract, following inexorably from the character of the primordial nature, but is concrete, the natural and spontaneous activity of the consequent nature integrating God's individual appreciations of the several occasions. (religion-online.org)