An involuntary action is one which occurs without the conscious choice of an organism. If it occurs specifically in response to a stimulus

Stimulus (physiology)

In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....

, it will be known as a reflex

Reflex

A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. A true reflex is a behavior which is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.-See also:...

.

Involuntary actions are opposite of voluntary action

Voluntary action

A voluntary action is produced by conscious choice of an organism. The organism, would in turn also be aware of the action while it is executed. This is the opposite of an involuntary action...

s that occur because of free will. Involuntary actions may or may not occur with the awareness of the organism performing it.