The Elder Scrolls Online: Tamriel Unlimited is the remastered version of The Elder Scrolls Online. The main difference between the two versions is switching from the subscription model to buy-to-play monetization along with several improvements and re-branding.
TES: Online is an MMORPG and the first multiplayer installment in the series. It's set on the continent of Tamriel, long before the events of offline titles. Following the tradition of the franchise, the story starts with you being imprisoned. You escape and start to search for the soul that was stolen from you. Besides the storyline, the game features nonlinear gameplay with multiple side quests, and you can freely roam around the world. In general, the plot is indirectly connected to previous TES titles, such as Morrowind and Skyrim.
In fact, The Elder Scrolls Online provides the same gaming experience as offline titles but shared with friends. You can widely customize your character, choosing from ten races and five classes and developing different skills and abilities.