What is a render parameter in IBM WCM and how it is related to the Plugin RenderParam?

Today, while I was reading the IBM WCM plugins documentation I found a plugin called The render parameter plug-in, which definition is formally: Use the RenderParam rendering plug-in to access public and private render parameters from your web content. Taken from The render parameter plug-in article in IBM Knowledge Center. So, these questions came into my mind: what is it…