A landing zone is a "safe" area in which a helicopter or other type of vertical take-off device would land. They are mostly used in war.
Images for kids
LANDING ZONE by John O. Wehrle, U. S. Army Vietnam Combat Artists Program Team I, (CAT I 1966). Courtesy National Museum of the U. S. Army.
LZ sign at Camp Dwyer in Afghanistan
U.S. Army troops practice securing a landing zone