曼昆电子版的《经济学原理（第六版）》和印刷版都在哪些地方有区别？
电子版书中有如下说明：
“Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.”

这其中“third party content"究竟指的是什么？请指教！