Echolocation is a way that some animals use to determine the location of things. They emit sound waves and listen for the echo. They use the delay to determine the distance. It is a kind of biological sonar.
Microbats find their insect prey in the dark this way. Whales and dolphins are two other kinds of mammals that use echolocation. Their sound waves go through the water, while the bats' sound waves go through the air.