4 Season Tents and 4th Season Tents

https://outdoorsfaqs.com/4-season-tents-and-4th-season-tents/
The term 4-season tent describes a shelter that is supposed to be suitable for all seasons. On the other hand, a 4th season tent is a shelter designed for winter and extreme conditions. So this is effectively a winter tent.

The main difference is the following: There are indeed true 4th season or winter tents on the market, but it is difficult to find true 4 season tents.