Lots of people don't know the difference between an assignment, TDY (Temporary Duty Assignment), and a "Deployment."
An "Assignment" is where one is permamently stationed. They remain at that base until they receive orders to move to a new base. A "TDY" is a temporary assignment, usually to attend a school, conference, temporarily help a unit which is undermanned, or participate in an exercise. When the mission of the TDY is complete, the airman returns to his/her permament duty assignment.
A "Deployment" is similar to a TDY, except the member deploys to be part of a specific operation, usually a combat operation overseas. Like a TDY, when the deployment is finished, the airman returns to his/her permament duty assignment. The Air Force deploys people to areas such as Afghanistan, Kuwait, Iraq, Saudi Arabia, Kosovo, and Bosnia for on-going contingency operations.
Under the Air Force's AEF (Air Expeditionary Force) concept, the Air Force's goal is not to deploy individuals and units for no more than 90 days in a year. However, the Air Force has a long way to go to meet that goal for personnel in many specific jobs. Most Air Force deployments last between 60 and 90 days.
Below is a chart that shows the average number of days deployed for airmen between the period of October 1, 2009 to September 30, 2010.