A legacy system is an old application, technology, mainframe, method, etc., still having an influence on an organization.
A legacy system is an old application, technology, mainframe, method, etc. that may or may not remain in active use, while still having a certain influence on an organization.
On one hand, maintenance of legacy systems and their integration with new solutions can be time consuming, particularly when a vendor's support is no longer available. On the other hand, legacy systems tend to be well-understood and thoroughly tested in production environments over the years since their deployment.
