Legacy System
An existing system that remains important but is difficult to change support or integrate using current needs and practices.
Plain English
Older or inherited software the organization still depends on.
In context
A system becomes legacy through context such as scarce knowledge unsupported dependencies rigid architecture or operational risk rather than age alone.
Example
“The billing migration must preserve data from the legacy system.”
When you'll hear this
- modernization
- integration planning
- risk review
Common misunderstanding
Legacy does not automatically mean useless poorly written or safe to replace immediately.
Also known as
legacy softwarelegacy codebase
Commonly used by
Related terms
Updated: 2026-08-27
