The reason it's a tricky question is because most of the time it's posed by people who have not given the first thought to running a website.

Either it's friends/relatives who are being polite but don't really care, or it's someone who wants a website but either (a) hasn't given any thought to what should go on it, or (b) has vague ideas about creating the next Facebook.

So in that first question, keep it short. "It's a way to manage a website." "It's like a website's operating system."

I've learned that if I ever say the word "content", for some reason, peoples' eyes instantly glaze over, which is problematic.

I will say that if your initial answer includes Jetpack, you have gone WAY too far. :)