Bigdei Kehuna (Priestly Clothing)
The Bigdei Kehuna are a set of garments worn by the Kohanim (Priests) as they perform their daily tasks in the Beit HaMikdash (Temple). A Kohen is forbidden to work in the Mikdash unless he is wearing all of the Bigdei Kehuna, but on the other hand cannot wear his Bigdei Kehuna outside of the Beit HaMikdash.
Regular Kohanim wear a set of four garments, while the Begdei Kehuna of the Kohen Gadol (high priest) consists of eight garments- the four of the regular Kohen plus four additional garments.
The four garments of an ordinary Kohen are the Kutonet (tunic), Michnasayim (trousers), Migbaat (hat), and the Avnet (belt).
The Kohen Gadol wears these four (although the hat of the Kohen Gadol is called a Mitznefet and has a slightly different design) and then also wears the Me’il (smock), Ephod, Choshen (breastplate), and the Tzitz (crown).