UFO stands for Unidentified Flying Object. It's any object seen in the sky that the observer can't identify or explain. If you spot something flying overhead and you can't tell whether it's a plane, a bird, a balloon, a drone, or something else, you've technically seen a UFO.

The term became famous in the 1940s and 1950s when people started reporting mysterious objects in the sky, often describing them as disc-shaped or moving in unusual ways. Many imagined these might be spacecraft from other planets. The idea of alien visitors captured people's imaginations, spawning countless books, movies, and television shows.

In reality, most UFO sightings turn out to have ordinary explanations. That strange light might be a weather balloon, an unusual cloud formation, a satellite, or even the planet Venus shining especially brightly. Military aircraft, experimental drones, and optical illusions account for many reports.

Scientists and military officials investigate UFO reports seriously, not because they expect to find aliens, but because unexplained objects in our airspace could be important for safety or security reasons. In recent years, the U.S. government has even released videos of genuinely puzzling sightings that pilots couldn't explain, though that doesn't mean they're extraterrestrial.

When something is a UFO, it simply means we haven't identified it yet. Mystery doesn't automatically mean aliens.