Red-Green-Refactor is a phrase created to help those practicing TDD (Test-Driven Development) remember the importance of the order of tasks. The premise comes from running the unit tests in some sort of GUI. When a test fails, the GUI displays a red bar. This red bar makes it easy to recognize that a unit test has failed. When a test passes, then the GUI displays a nice green bar.
The first thing to accomplish is to write a failing test (Red bar). This proves that the test is a valid test and will fail when the code is not implemented correctly. Once a red bar can be reproduced, just enough code to get the test to pass (Green bar) is written. The green bar is now a safety line. The new goal after the green bar is to refactor the code while keeping the green bar. Now that the safety line exists, as much time as needed can be spent on the refactor. After the code is refactored, then the process starts all over again.
I like to call it R~e~d/Green/R~e~f~a~c~t~o~r as the least amount of time is spent making the bar green while the most amount of time is spent refactoring and creating the test.