How to make tanking fun.

[Shurrikhan]

I don't believe that to be correct.
While I hate to point to WoW related things in regards to defining things in MMOs, this gives a decent general overview of the idea of active mitigation through the lens of WoW.
https://wow.gamepedia.com/Active_Mitigation

"With Mists of Pandaria the various tanks gained short-cooldown abilities that embody active mitigation. Tanks who use these abilities optimally will be able to overcome challenges that would defeat a less skilled tank."

"The term "Active Mitigation" now refers to a single, specific ability that a Tank must use as a counter to specific Boss abilities. These Boss abilities are designated as Mitigation Checks."

I have to agree with Kalise on this one. Active mitigation typically has to be something that is not reserved for express use. If it could, it wouldn't require any active efforts on the player's part to prepare for the coming damage, merely a timer of sorts. There has to be an integral means of compromise available to be manipulated, decisively and timely, towards mitigation.

How WoW decides to redefine the term as in order to offer additional gimmicks and continue not to have much actual active mitigation is of no consequence to its typical meaning.