The term 'UFO RIDER' is a combination of two words, 'UFO' and 'RIDER'. The first word, 'UFO', stands for Unidentified Flying Object, which is an object that cannot be identified by the observer. The second word, 'RIDER', refers to someone who rides on or in a UFO. The crossword solution for this term is 'ALIEN', which refers to an extraterrestrial being from another planet. An ALIEN is typically depicted as having an advanced technology and a mysterious origin.