My understanding is a cloudpage is a way to create a webpage using html/css/js. From what I can see a microsite is the same thing. Is there a difference?
A microsite is a collection of one or more landing pages hosted in your account. Use a microsite to contain information beyond what you include in an email. For example, you can create a microsite to contain a lead-generation form, an opt-in subscriber form, or to direct subscribers to more information about a corporate initiative. A larger distinction is that allows to host landing pages in your designated account.
So when you say Microsite, there are two versions of Microsites -- the Classic version or CloudPages Microsites. Both essentially just tie together landing pages/Cloud Pages in a site map.
The classic version of Microsites uses landing pages in classic content. CloudPages Microsites is the newer version.
Similar to Content Builder versus Classic Content, CloudPages uses a WYSIWYG editor within the tool