If you are new to openSUSE, then we recommend that you spare a few minutes to read this first. 😉
Leap is binary compatible with SUSE Linux Enterprise. Its major release aligns with SUSE Linux Enterprise releases which are supported for about 36 - 48 months. A minor release (e.g Leap 15.1, 15.2, etc) is expected to be available every year. The minor release aligns with SUSE Linux Enterprise Service Packs. Thus, openSUSE Leap 15.2 is said to be binary compatible with SLE 15 Service Pack 2.
If you have a machine running openSUSE Leap 15.2, you can buy a support license from SUSE and switch to SLE 15 SP2 without having to re-install. The other way round is possible too, i.e switch from SLE to openSUSE.
The Leap version number is defined as Leap major_version.minor_version.
Tumbleweed is a rolling distribution. It contains latest stable versions of software. Rather than waiting for a periodic release cycle, Tumbleweed makes the newest stable software available as soon as their they pass the openQA tests and are ready to leave the Factory repository.
New updates keep coming in Tumbleweed, sometimes several times per week. Users who rely on third-party kernel driver modules (e.g graphic drivers) will have to update the drivers from source on their own every time the kernel version changes (this happens often). It is advisable not to use Tumbleweed if you have such hardware driver concerns.
The above image describes the development roadmap and relationship between Tumbleweed, Leap and SUSE Linux Enterprise.
Tumbleweed is available as a DVD image or you may try it out using the LiveCDs.