'action or intervention, esp. such as to produce a particular effect' : "canals carved by the agency of running water" … or 'a thing or person that acts to produce a particular result' (Apple 2.x dictionary)
Agent (with autonomous causality) and actant co-constituting each other?
Agency can be an important idea in that, conceptually and philosophically, it can lead to finding ways to individual freedom for you (or I). If you find yourself bound in, in some ways, think through the implications of agency for yourself.
See, too -
California condor: What's anthropological agency? I heard a fascinating, Anthropology talk yesterday at Stanford, which suggested that food in Bengal, India, was an actant, or had agency, What's an agent anthropologically?, What's agency philosophically? What's agency for robotics? When can we say that a robot has achieved various degrees of autonomous causation? What's agency for digital bots such as avatars in virtual worlds?
Again and further, what's agency vis-a-vis the academic field of Anthropology?