What's the difference in ASP.NET MVC of RedirectToRoute and RedirectToAction?

Redirect to route looks up the route table thats defined in global.asax and redirect to action redirects you to a specified controller/action.

that's about it really

RedirectToRoute means it redirects to a specific URL which is defined in routing API.(Global.asax)

RedirectToAction will return a http 302 response to the browser and then browser will make GET request to specified action.

Ideally I would use RedirectToRoute for Action Links/Images and RedirectToAction in Controller's Action to redirect to another Controller's Action.