Kusazuri (草摺) are the plated armor skirt commonly seen on traditional Japanese samurai armor. They are composed of a grid of small plates (lamés) made from laminated leather or iron and riveted together in a fashion similar to sode shoulder guards.
Their role is to protect the waist and upper thighs while still giving flexibility, much like their Western equivalent, faulds and tassets.
A related piece of armor is the haidate, a set of similarly-constructed thigh guards worn underneath the kusazuri but affixed directly to the thighs instead of swinging freely.
The simple cloth equivalents found on kendo bougu training armor are called tare.