The word Tank has been used in online games for many years, to describe the component of a fighting force that has high hit points and/or defense. Usually Tanks use this asset in combination with abilities or tactics that draw the fire of enemies away from units with less hit points.
While any cards with high hit points can be a tank in the first sense, and tactical usage is a matter of skill, there are a handful of cards that can Provoke enemy units into attacking them. Among the other uses of Provoke is the aforementioned drawing away of enemy fire from lower-hp units. Provoke cards include Lightblade, Lost Grigori, and Grinder.