Have most Imams declared a holy jihad against infidels, and that killing them assures them a place in heaven?

I have been told that most Imams and clerics of Islam have declared a holy jihad (Holy war) against the infidels of the world. And, that by killing an infidel, which is a command of all Muslims, they are assured a place in heaven. If that is the case, can you give me a definition of an infidel. If that is not the case or if you have more to add, please explain.