grey alien

Short definition from Wiktionary

Noun

1. 1
   An archetypical humanoid alien, usually described as having grey skin, elongated, hairless, sexless features, and a large head with bulbous black eyes; chiefly associated with flying saucers, alien abductions and conspiracy theories relating to cover-ups by the United States government, such as Area 51.
2. 2
   Used other than figuratively or idiomatically: see grey, alien.