Sound waves can be reflected. They most often reflect when they hit an obstacle in their path, such as a hard wall. Some sound waves will be reflected when the sound transitions from traveling through one medium to another, such as going from air to water.
The rest of the sound waves hitting a different medium will be transmitted through the medium and continue traveling. When a sound wave is reflected, an echo or reverberation can result. The difference is in the brain's perception of the sound wave as a different sound or as a prolongation of the same sound. The brain retains the perception of sound for a tenth of a second after the sound has struck the eardrum. If a reflected sound wave hits the ear before that period of time is over, the sound is perceived as reverberation and part of the first sound, but if it is heard after that period is over, it is perceived as an echo.