The action one needs to take on a document; also the type of action that is requested by an Action Request. Actions that may be requested of a user are:
Acknowledge: requests that the users states he or she has reviewed the document.
Approve: requests that the user either Approve or Disapprove a document.
Complete: requests the user to enter additional information in a document so that the content of the document is complete.
FYI: intended to simply make a user aware of the document.