The term 'sonar ECHOES' is a combination of two words, 'sonar' and 'ECHOES'. Sonar stands for Sound Navigation and Ranging, which is a technique used to detect objects underwater by sending sound waves and measuring the time it takes for the sound waves to return. The returning sound waves are known as ECHOES. Therefore, sonar ECHOES refer to the sound waves that are reflected back after being sent out by sonar technology.