As for theists, the gods are equally undefined for atheists/agnostics. For an igtheist, beliefs of atheists/ignostics (or lack of belief) cannot be taken any more seriously than those of theists, until definitions are provided.

Take an example. There are people who say that god is nothing but merely energy. Can someone call herself an atheist if this is definition of god?

Sans definition of god, theism/atheism do not make sense.