A lens which focuses light rays from a source into parallel paths, thus focusing the image relayed at infinity. Highly useful in Head-Up-Display systems, for obvious reasons.
This will be the 2nd in my series of largely useless technical jargon, which will continue as it is more fun writing this than writing a report on the performance and aerodynamics of an MAV.
-For more amusing and less contrived definitions, look up my ones for France or Europe. They're OK.