A REPL is the foundation of the Clojure coding experience. The REPL provides a runtime environment where you can instantly get the results of evaluating your code. You can write code in a REPL too, although typically code is written editor and sent to a REPL to be evaluated. When you start coding, the first step is to run the REPL and keep it running until you are finished.
A REPL is the same environment used for running your Clojure applications too.
Lets look at the newest and fastest approach to running a Clojure REPL, the Clojure CLI Tools and rebel-readline.