When people ask me what OR is, I say it's "mathematical modeling and computer simulation" or "system analysis and optimization" or just "optimization".
Good resource for OR fellows to fish for some nice examples and descriptions:
At a graduation ceremony a couple of years ago, the chair of the OR department at Cornell said that OR is "the math, modeling, computer science and engineering of making decisions in often uncertain environments." I'm paraphrasing, but I thought that was a pretty good definition.
I love having studied OR; I would love for it to have more name recognition so that it wouldn't be so hard to explain!
Good resource for OR fellows to fish for some nice examples and descriptions:
http://www.scienceofbetter.org/