Your website can bring in content from lots of different sources. Embed video, slide presentations, flip-books - there are endless possibilities. The content can be something you have created or just as easily content produced by others for you to share.
A Presentation Example
You will find plenty of examples of embedded content on this site. This one is from Slideshare.
A special 'gotcha' to be aware of:
Not all embeddable content will play nicely on all devices. A particular problem is with Apple devices (iPad, iPhone, iPod) that do not support Adobe Flash Player. These devices will not show the content. Most online sharing systems content have taken this into account now and have that sorted. However it worth checking before using a particular service.