brownfield
/BROWN-feeld/ · noun · Development · Origin: 2004
Definitions
A software project built within the constraints of existing systems, codebases, and infrastructure, as opposed to a greenfield project that starts from scratch. Most real-world software development is brownfield — working around legacy decisions, maintaining backward compatibility, and gradually modernizing while keeping everything running.
In plain English: A software project where you're working with and around existing code and systems, not building from scratch — which is most real-world programming.
Example: Every exciting greenfield project eventually becomes someone else's brownfield nightmare in about three years.