What are 'bunker buster' bombs that US used to hit Iranian missile sites?

US forces used 5,000-pound "bunker buster" bombs to strike Iranian missile sites near Strait of Hormuz. Bunker busters are built for a narrow set of targets. Their purpose is to destroy hardened or buried structures that cannot be neutralised by surface explosions alone. In 2021, it was reported that US Air Force had successfully tested GBU-72/B bunker buster bombs.