Refpeople - Social Network is a Content Curating website. One of the main purpose of Content Curating is to group, structure and organize the best and more relevant online content related to a given topic or subject. Doing so, it's easy for people to find what they are looking for.
The first level of this content organization is to link everything to a Topic then add to this topic all the related content (video, image, link, blog,etc.). Here is an illustration of the difference between Topic and Post.
Let's now sum up this illustration to make it more clear.