How do you define low-hanging fruit?
The interviewer is testing you to make sure you're knowledgeable about relevant terminology. Prior to the interview, brush up on various product manager terms and concepts so you can easily answer these kinds of questions. Be direct, and give examples whenever possible.
"I'd say that low-hanging fruit is simply a quick win. In other words, what can we get a lot of value from with very little effort? In many cases, it's a product feature that is easy to add yet will drive lots of revenue. Other times, a target market might have a straightforward need that is easy to fill. Sometimes these opportunities suddenly appear after there's been a change in the market. As a product manager, it's important to pay attention to market opportunities that arise and to the feedback you're hearing from customers so you can move quickly and grab that easy low-hanging fruit."