Subversion is a legacy source code control system. It is run by the Apache foundation.
Subversion exists to be universally recognized and adopted as an open-source, centralized version control system characterized by its reliability as a safe haven for valuable data; the simplicity of its model and usage; and its ability to support the needs of a wide variety of users and projects, from individuals to large-scale enterprise operations.
While much of the world has moved over to Git, Github, and Gitlab, Subversion still has its uses. For example, WordPress plugins require the use of a Subversion repository.