Kusazuri (草摺) are the plated armor skirt commonly seen on traditional Japanese samurai armor, attached at the bottom portion of the dou, the chest 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.
This tag implicates japanese_armor (learn more).