The openSUSE Factory project is the development codebase that creates openSUSE Tumbleweed, which is the rolling-release version of the openSUSE Project. The Factory receives a constant flow of packages from developers working on the openSUSE distribution.
The Factory repository holds the raw, untested packages and they receive automated testing via openQA. Once the testing is done and the repository is deemed to be integrated, stabilized and consistent, it is synched to the download mirrors, and two or three times a week it is published as openSUSE Tumbleweed.
The Tumbleweed version is primarily used by power users, software developers, and openSUSE contributors who need to work on a reliable platform that is as close to openSUSE Factory as possible. The Linux kernel is frequently updated in Tumbleweed, so users who rely on 3rd party kernel drivers often need to update all their drivers from source whenever they download a fresh version of Tumbleweed. Users who just need a reliable, stable working version of openSUSE and don’t want to worry about compiling kernel modules prefer to use the openSUSE Leap version of the distro, which is updated much less frequently.