A protocol that sends a message to another computer and waits for acknowledgment, often used to check if another computer on a network is reachable, A high-pitched, short and somewhat sharp sound, a sharp high-pitched resonant sound (as of a sonar echo or a bullet striking metal), verb_ sound like a car engine that is firing too early, To send an email or other message to someone in hopes of eliciting a response, networking A packet which a remote host is expected to echo, thus indicating its presence