What is the meaning of Rear_admiral_(lower_half)?

A commissioned officer in the United States Navy, Coast Guard, NOAA Corps, or PHS Corps of a grade superior to a captain and junior to a rear admiral (upper half). A rear admiral (lower half) is equal in grade or rank to an Army, Marine Corps, or Air Force brigadier general.

A naval officer of equivalent grade or rank in the navy of other countries, such as commodore.

Source: wiktionary.org