It depends on who I'm talking to and how much time I have.
Option 1: I tell them that I manage our email marketing and database management. Then 90% of the time they follow up with "Oh, so you send spam." I then respond by saying that it is actually my job to make sure we don't send spam
Option 2: The analogy approach...I ask them if they've ever shopped online and put things in their shopping cart without buying the items. Then a few hours/days later they get an email saying "Hey, did you forget to check out?". I then tell them I coordinate and build the programs needed to make all of that happen. Even though, no company I've ever actually worked for used e-commerce, it is a way for them to understand on a very high level what I do.