There is even a difference of what zen is from master to master. The problem with defining zen, illumination and other similar concepts, is, according to a lot

There is even a difference of what zen is from master to master. The problem with defining zen, illumination and other similar concepts, is, according to a lot of teachings, that words are inedequate tools to describe them. Practice and experience is what get you closer to what it is. It's pretty hard to agree on something you can't talk about. We already have a hard time agreeing on things we have metrics on.