Greeblies are usually "found" parts that are added to a costume to give it added detail. Greeblies can be anything from a plastic model piece, to a piece of electronics.....
The Greeblies were a German punk band, circa 1968-1971. They had a small cult following of devoted fans here in the states who changed fashion history forever by gluing small, seemingly random bits of junk all over their clothing. These fans, calling themselves "Greebs", were known to run wild after concerts, accosting innocent passers-by, shouting incoherently, and doing generally naughty things.
The band's leader, Myopis Punderheimer, encouraged these antics, stating once, "Hey, it's all about the bits and pieces, isn't it?"
Sadly, the band broke up, choosing to follow "Solo" projects.