In ufology, Greys, also known as Roswell aliens, Zetas, and Reticulians, are aliens or extraterrestrial life forms that appear in purported modern day encounters and other UFO-related paranormal phenomena. Said to be one of several species of aliens, greys make up approximately 75 percent of all aliens reported in the United States, 20 percent of all aliens reported in Continental Europe, and 12 percent of all aliens reported in Great Britain. Typically, Greys are described as being either approximately 120 cm (four feet) tall or over six feet tall, with grey (sometimes blue-grey/green-grey) skin. Their body is typically described as being elongated, and lacking in muscular definition. Their legs are shorter and jointed differently than one would expect in a human, giving them an apparently awkward gait. Their arms often reach down to their knees, and some accounts give them three digits, or three digits and a thumb on each hand. They have a bulbous, hairless head supported by a thin neck, which is dominated by large, (usually black) lidless eyes. They typically have small flat noses, small mouths and small ears lacking a pinna. In some cases, Greys are said to have slit-like nostrils on a flat face. _Wikipedia
Written about extensively by authors Whitley Strieber and Budd Hopkins.