A pulsar wind nebula (also known as "plerion", derived from the Greek word "πλήρης" ("pleres") meaning "full"—a term coined by Weiler & Panagia [1978]) is a nebula powered by the pulsar wind of a pulsar. At the early stages (first few thousands of years) of their evolution, pulsar wind nebulae are often found inside the shells of supernova remnants. However, pulsar wind nebulae have also been found around older pulsars whose supernova remnants have disappeared, including millisecond radio pulsars (e.g. Stappers et al. 2003). A prototypical pulsar wind nebula is the Crab Nebula (Hester et al. 2008).