If I can't see their profile is their account deactivated?

I come across accounts from time to time, who's profiles I cannot see.. There is no link to see them.. have these people deactivated their accounts? Do some people only activate accounts to post and then deactivate until they want to post again? or is it something else??? I am confused.

I think it's an option people can set to make their profile private. I'm not sure exactly how to do it, all I know is a few of my friends have their accounts set that way.