Definition: Legacy code is existing software that is still used but relies on older technologies, designs, or practices and may be difficult to maintain.
It does not necessarily mean “bad code”—it simply means the code has become outdated relative to the current environment.
Examples:
- A company’s application still runs on a programming language no one uses for new projects.
- A 15-year-old system that still processes millions of transactions.
- An old application that depends on an unsupported library.