Agency refers to the ability to act or perform an action.In contemporary theory, it hinges on the question of whether individuals can freely and autonomously initiate action, or whether the things they do are in some sense determined by the ways in which their identity has been constructed. Agency is particularly important in post-colonial theory because it refers to the ability of post-colonial subjects to initiate action in engaging or resisting imperial power. The term has become an issue in recent times as a consequence of post-structuralist theories of subjectivity. Since human subjectivity is constructed by ideology (Althusser), language (Lacan), or discourse (Foucault), the corollary is that any action performed by that subject must also be to some extent a consequence of those things. For the colonial discourse theory of Bhabha and Spivak,which concurs with much of the post-structuralist position on subjectivity,the question of agency has been a trouble someone.However,many theories in which the importance of political action is paramount take agency for granted.They suggest that although it may be difficult for subjects to escape the effects of those forces that ‘construct’them,it is not impossible.The very fact that such forces may be recognized suggests that they may also be countermanded.

Source: ASHCROFT, Bill et al. Post colonial studies : the key concepts. New York: Routledge, 2007. (link)