Safe space?

What the hell is a "safe space"?  It's an expression I hear more and more these days, but it's not explained and the assumption is that "everybody knows" what it means. As it seems to be mostly associated with Universities, I asked my grand-daughter who is in her third year at a Midland University that perhaps I'd better not name.  In essence, she said, it's the opposite of open discussion.  It's a way of shutting up anybody who disagrees with your point of view.  You get some particular place or event officially designated a safe space on behalf of some group (usually feminist or pro-LGBT) and then you can forbid entry to anyone who you think might seek to say something you don't want to hear.  It's a sort of comfort blanket for whacky weirdos (her words, not mine).