GHCi is the interactive environment for the Glasgow Haskell Compiler (GHC), which is a popular compiler for the Haskell programming language. It allows users to write and test Haskell code in real-time, making it easier to experiment with functions and concepts without needing to compile a full program. In GHCi, users can load Haskell files, execute expressions, and explore libraries interactively. This tool is particularly useful for learning and debugging, as it provides immediate feedback on code changes. GHCi supports various commands that enhance the coding experience, such as loading modules and inspecting types.