A brigandine is either an armless leather jacket or a thick, fabric vest similar to, but not as thick as, a gambeson, to which a lot of metal plates have been riveted. Usually, the plates are on the inside, giving the brigandine it's characteristic "studded" look as the heads of the rivets show on the outside. The brigandine offers great protection for the abdomen and it's a reasonable compromise between a gambeson and a breastplate. This particular brigandine is sleeved with padded maille.
The brigandine is one of the most common forms of heavy armor worn by rich soldiers. Most soldiers still wear padded maille, but those with more economic freedom usually opt for a brigandine for its superiour defenses.
Coupled with the brigandine is a sturdy full helm as well as adequate shin guards to protect the legs. This is the pinnacle of armor technology of the day.