What is "close helmet"

n. A helmet that entirely covers the head, including the face.

The close helmet, also called the close helm was a military helmet worn by knights and other men-at-arms in the Late Medieval and Renaissance eras. It was also used by some heavily armoured, pistol-armed, cuirassiers into the mid 17th century. It was a fully enclosing helmet with a pivoting visor and integral bevor.