What does fundamentalism actually mean?

[Ross]

I looked at various definitions of what religious fundamentalism is, but I still can’t wrap my head around it. Does it basically mean that you are too religious? 
 

Also, I am aware that Western Europe has little to no Christian fundamentalism, but most of their population identify as atheist. Is that what non-fundamental religion will look like. If that’s the case, would it be appropriate to say that Western Europe is just no longer “Christian”, and not “Christian fundamentalist”?