Delay is an audio effect where a recorded input is played back after a certain amount of time has passed. In essence, it is an echo effect. Delay is a very simple effect compared to something like EQ or compression. Typically, there are only a few parameters to adjust. These parameters simply determine the amount of delay and when the signal will play back. For example, you could have a grand piano with the delay set on eighth notes. In this case, the piano notes will play back, or echo, each eight note after the initial input. Furthermore, there will be more parameters for how strong the delay will be (dry/wet) and how much echo will ultimately be heard (feedback). Delay is simple but can be used for many different things. A common misconception is that delay is only used for instrumentation. However, in today’s music production delay is very common for vocals. Delay is great for creating the feeling of space or distance.
Music Production - All You Need To Know 