Comfort zone word is basically used for those people who don't dare for anything & you can say it's used for those who feel insecure.
Comfort zone is nothing but a virtual world around you, in which everything is managed according to your thinking & habits.
If you will observe some lazy or dull type of people around you, then what they r doing is called living in COMFORT ZONE. If you will ask them to do anything daring or anything which needs some efforts, they will simple deny it. They will make arguments against that task and they will try to avoid it.