Ah yes, the new way of turning a lot into a seasonal lot. Where it will host the holiday events of each season.

The season mark has been patched with the preparation for enlargement seasons in the base game The Sims 3. This will ensure that land with that tag will work correctly if they are installed in an installation without the extension seasons. In that case, they are shown with their usual appearance (common mode).
In addition, contractors may also without the possession of seasons to prepare their land for other players for different seasons.


Source: SimTimes