It can occur it the aircraft is over-rotated on takeoff before actually lifting off the runway or over flared on landing (usually with too slow a speed). The tail strikes the runway before/simultaneous with the mains lift off on t/o or before/simultaneous with the mains touching down on landing, hence "tailstrike".
Aircraft that have minimum tail clearance when rotated for t/o or flared for landing usually have some sort of "tail skid" to protect the lower aft fuselage in the event of a tailstrike. The most visible example that comes to mind for a common aircraft is the Boeing 727 - the tailskik actually extends when the gear is down and it is easily visible. The Concorde had a similiar arrangement, which even appeared to incorporate a small wheel - would that be called a "tail wheel" instead of a tailskid?

.
You can go to airliners.net and search for "tailstrike" and/or "tailskid" to see some pictures.
Jim
[post="299702"][/post]