I've been giving this a lot of thought recently. And, being who and what I am, realized I classify them. Roughly:

There are False Flats. You don't really know you're going up until you turn around and go down faster.

There are Inclines that only need a slightly lower gear to handle.

Hills are those grades that terminal velocity going down is > 20 mph.

%$*@!! Steep is when I have to get off and push.

I have come to terms with all but %$*@!! Steep. Those still bother me. A lot.