Not format per se. 360° photos are regular photos you can open in any viewer, and 360° videos are regular videos you can play in any player.

But the 360° sphere is projected onto the flat medium in different ways, and the viewer or player needs to understand how to reproject and render the part of the image you're looking at as a flat rectilinear view depending on your point of view - and of course it should let you change the POV.

You can see various types of projections here. The most common is probably equirectangular.

When I share photos online, I use a Javascript-based player called Pannellum. When I share videos, I use a player called VideoJS - itself called by Pannellum. And I also split my videos into smaller chunks so they don't violate the GitHub repo file size limit, since I host all my material on GitHub.