Ghasts are large, floating mobs found in the Nether, a dangerous dimension in the game Minecraft. They resemble white, ghostly creatures with large eyes and can fly around, making them difficult to hit. Ghasts are known for their distinctive, mournful sounds and their ability to shoot explosive fireballs at players. When a ghast is attacked, it will retaliate by launching these fireballs, which can cause significant damage to players and the environment. Players can defeat ghasts to obtain Ghast Tears, a valuable item used in crafting potions and other recipes. Their presence adds an element of challenge to exploring the Nether.