What is the difference between active and passive sidestick?
For references, I've used United States Patent Application 20080156939; BAE Systems Develops Civil Aircraft Active Control Stick; Active and passive side stick controllers in manual aircraft control; &amp; the Side-stick wiki entry. The wiki is a general side-stick discussion listing (some) aircraft that have side-stick fly-by-wire (FBW) technology, but does not go into active vs. passive.

Generally speaking, if you have used a joystick on your PC to fly Microsoft's Flight Simulator, such as Microsoft's Force-Feedback Sidewinder Pro, you've used an active side-stick.

According to the Patent Application cited above, the patent is for an Active Side-Stick technology described as "pilot flight control stick haptic feedback mechanism provides variable force feedback to the pilot flight control stick." One of the 'issues' with the current passive side-stick technology (approved for use) used on aircraft such as Airbus' A380 is that there is no tactile feedback when using the side-sticks, such as a pilot would feel using an old-style column or yoke. In a Cessna 172, for instance, when you pull/push/turn the yoke, there is actual tactile feel, if you pull back strongly in-flight, you'll 'feel' the forces exerted against the airflow. Passive side-sticks have none of this 'feel'.

Active SS technology attempts to replicate the forces on the joystick.

Active SS technology is currently used on most miltary aircraft using side-sticks, but does not appear to have yet made its way into civilian airliners.

(If I've gotten stuff wrong, I'll remove/fix this answer, as I am not an airline pilot and have never had the opportunity to fly military hardware.)