Serendipity: an aptitude for making desirable discoveries by accident (dictionary.com)
I find quite enjoyable searching the web for new contents about interaction design: projects, ideas, methods and even definitions. And I usually do it with good results. This morning I was having a look into youtube. I have found an interesting video by Richard Ziade, where he gives a very clear and direct definition of IxD:
the design of interactions, specifically interactions between people and things. The design thinks about the dialogue and the flow the person is going to have with the products she buys.