Q: What does ERR_CONNECTION_REFUSED mean and how can I fix it?

I have a Macbook OS X Yosemite version 10.10.3 and recently every time I try to look at a webpage, this page comes up:

Some webpages work, like YouTube and Wikipedia, but most others don't. What does ERR_CONNECTION_REFUSED mean and how can I fix it?

I have tried restarting the computer and restarting Google Chrome app that I use but haven't had any success.