The Last Stable Release has all the latest enhancements and bug fixes for Weave. This is in contrast to a Weave Pre-release which could be seen as "unstable" and likely to change before it's released, and therefore not supported.
Currently the Long Term Support Release is 2.5.15. If there are any bug fixes they are applied to the Last Stable Release and the Long Term Support Release. If there are enhancements, they are only applied to the Last Stable Release.