There are many types of relays in swimming. The two main categories are Medley Relays and Freestyle Relays. A medley relay consists of 4 swimmers, with each swimmer doing a different stroke (Backstroke, butterfly, breaststroke, freestyle). A freestyle relay consists of 4 swimmers, with each one swimming freestyle.
A 100 relay would mean that each swimmer is going for 25 yards/meters. A 200 relay means 50 yards/meters each and so on.
Sometimes relays are referred to as "four by (length)" relays. So a 400 yard freestyle relay consisting of four 100 yard freestyle legs would be called a "four by 100 yard free relay" and so on...and so on also swimming is an awsome sport!!!!!!