What does REPL mean?
REPL stands for “Read–eval–print loop”.
“A read–eval–print loop (REPL) is a simple, interactive computer programming environment. REPLs facilitate exploratory programming and debugging because the read–eval–print loop is usually much faster than the classic edit-compile-run loop. In a REPL, the user enters one or more expressions (rather than an entire compilation unit), which are then evaluated, and the results displayed. The name read–eval–print loop comes from the names of the Lisp primitive functions.” (source)
More info here.