Just another spelling for "gray" in pluralis. Grays (sometimes spelled "greys") are supposed to be extraterrestial intelligent non human beings who are captured and held in secret labs deep within Area 51 and perhaps the Cheyenne Mtn base.

In Sweden, the word "grejs" is translated to "a lot of physical things stuffed up all around the office".

A derogatory term used in reference to a silicon (Si, Atomic number 14; atomic weight 28.086; melting point 1,410°C; boiling point 2,355°C; specific gravity 2.33; valence 4.) based extraterrestial lifeform.

The term gained popularity among human beings because of its ability to describe both the chemical makeup of the aliens' genitalia while simultaneously referencing the fact that they are all a bunch of pussy cunt bitches. God, I hate Silicunts.

Game series, based off of UFO lore as well as own made up stuff. Original came out in 1994, with Terror from the Deep coming out in 1995, and Apoclypse in 1997 as direct descendents. There are other games based in the same universe, as well as two planned but cancelled games named Genesis and Alliance.
PC Gamer has the original free in its 2000 september disc.

As a word it can be used to describe any type of alien defense force, as X-Com comes from a 3 word phrase of close meaning.

Large, extraterrestial beings who are from Outer Space. Those lucky enough to be able to communicate with these large bugs are able to command them to rape people they dislike up the butt.

Marvin the Martian

ancient flying machine resembling todays ufos, some people says this is a proof of extraterrestial visitors in the past, the word from sanskrit has several meanings ranging from temple or palace to mythological flying machines described in Sanskrit epics where several passages refering to this objects are made.

Area 51 FAA's formerly secret airport at Groom Lake, Nevada called Homey Airport