MS 365 is rebranding of Office 365. It is the same product.

It is the subscription, perpetually being updated, version of Office. It has been around since at least 2013. It has has its good and bad points. For regular work, I think I would recommend one of the perpetual license versions. However, even they get sometimes surprising changes to the user interface.

If you have a group of people using Office, Microsoft 365 Family, is the least expensive way to go, so long as they are all connected regularly to the Internet.

This is a late reply posted in case anyone else finds this post.