"Human action is purposeful behavior. Or we may say: Action is will put into operation and transformed into an agency, is aiming at ends and goals, is the ego's meaningful response to stimuli and to the conditions of its environment, is a person's conscious adjustment to the state of the universe that determines his life. Such paraphrases may clarify the definition given and prevent possible misinterpretations. But the definition itself is adequate and does not need complement of commentary."
I might phrase the action axiom this way: the concept of "action" is a useful lens by which to describe the phenomenon of experience; the concept of "action" presumes that a subject acts with purposes in mind; that action presumes a subject selecting from possible action-means, to achieve an end preferred by the subject.
Just as the geometrical definition of a triangle, may at first glance seem unimpressive but when deductive reason reveals the implications of the Pythagorean theorem, the seemingly simple definition reveals itself to have impressive implications. In the same way, the recognition of the definition of action as purposeful behavior which presumes that a subject acts as a means to achieve and end/purpose, this simplistic definition can reveal such implications such as: persons engage in economic trade/exchange, so as to meet their predicted preferred end-state/outcome, therefore every consensual/voluntary exchange takes place because both person expect to be benefitted from the exchange and that both parties may benefit from the exchange because they each have slight to extreme differences in their subjective valuation of what they give in exchange versus what they receive in exchange.
To say that, "Bob acts to mow his lawn by pushing a reel-mower, in order that Bob may achieve his preferred end-state, which is a mowed lawn.", is more meaningful than, "Hominid known as 'Bob' exhibits behaviors in such a way, such that he pushes a mechanical device around an area of short grass and one can observe that that in this process, some of the short grass is shortened."
This later analysis, rejecting action as purposeful behavior, must see only behaviors without purpose; behaviors just *are* and may have no reason or meaningful causes or purposes. The later analysis may be seen as less meaningful, because the observer of Bob exhibiting behavior, is herself only exhibiting behavior; which is to say, that without the lens of action as purposeful behavior, then the scientist making observations does not do so for any rational purpose but the scientist herself is only exhibiting behavior.