What does "Does your app contain, display or access third-party content?" mean for me?

While submitting a new app to the App Store I got this question: "Does your app contain, display, or access third-party content?". Can I answer yes to this question and still submit an app? Does answering yes mean that I have to show confirmations from the creators of the third-party content that I can use it in my app? If for example my app is Twitter - would I have to answer "yes" in this case? If so, how could I prove that I have the rights for all content published in the app?