In asking this question, your interviewer wants to know that you are capable of explaining complex ideas without being condescending to your colleagues or clients and that you don't talk over their heads. Give them an example of how you break down information to make it more easily digestible for the average person. If it helps, try to think of a presentation about a complex topic, such as a proposal to solve a challenging problem. The solution may seem obvious to you, but everyone else in the room is scratching their heads trying to figure out what you're talking about. When you can define key terms and phrases to make them more relevant to your audience, you have skill! Not everyone can do this. Prepare an example that demonstrates your communication skills and your ability to convey complex information in easy to understand terms so your interviewer gets the sense that you will be able to.