What is the gradient-flows tag for? It has no tag wiki. There are relatively few questions using this tag, and I'm not sure how they relate to each other.
If a tag is good enough for Tao, it's good enough for MSE.
Seriously: although I'm not a fan of tags named after mathematical objects (rather than areas), this one appears to be used correctly: for dynamical systems of the kind $\dot x=-\nabla U(x)$, where $x$ can be a vector, or a function, or a point on manifold, or a manifold itself... There is a certain common theme here, although the problems come from several fields: PDE, Riemannian geometry / geometric analysis, calculus of variations, some applied math (e.g. image processing).