Delay is probably one of the most valuable effects. It is the building block that many other effects such as reverb, flange and chorus are built from. A delay is basically what the name says. It is a delay of the original signal of the guitar that plays at a set time after the original notes or chord is sounded. It can range from milliseconds to several seconds depending on how you set the time parameters. Set at several seconds you can actually solo over yourself. Slapback delay is probably the most commonly used and can range from 30  milliseconds
to 100 milliseconds. Delay is a fun one to play around with and it can add warmth to a dry sound