REPL stands for Read-Eval-Print-Loop - however, the function of REPLs at Repl.it has outgrown that definition. Capable of doing much more, Repls are the workspaces that Repl.it users interface with whenever they use the app.
A Repl at Repl.it is an interactive programming environment. You can create a workspace in any number of languages, where you are given a container on a virtual machine where your code can run, sandboxed. In any given repl, there are two main parts - the editor and the console.
The console is where the standard output will appear, and where you will be prompted to enter standard input. In most languages, the console doubles as a repl - you can evaluate snippets of code interactively, and in some cases, you can interact with variables that have been defined in your main body of code.
Read on to see what Repls are capable of.