"X-COM: UFO Defense" is a tactical strategy game released in 1994, where players manage a global defense organization called X-COM to combat an alien invasion. Players must research alien technology, build bases, and train soldiers while responding to UFO sightings and abductions. The game features turn-based combat, allowing players to control their soldiers in battles against alien forces. Success depends on strategic planning, resource management, and adapting to the evolving threat posed by various alien species, making it a classic in the strategy genre.