These tough, limpet like creatures were originally thought to be inedible. However, pioneering colonists discovered that a combination of high pressure and chemical treatment in an ammonia-based solution could render these iron rich creatures into a digestible and delicious food source. They are now considered a delicacy around their galaxy.
— In-Game Description
It is a rare commodity, so increases in value the further you take it from its point of purchase.
A greeble is a small piece of cosmetic detailing added to an otherwise flat or plain object to make it more visually interesting.