I spent five minutes on the site and couldn't find a single link that lead to a section saying "ThingSpeak is...". So what is this? An API framework for use

I spent five minutes on the site and couldn't find a single link that lead to a section saying "ThingSpeak is...". So what is this? An API framework for user-facing devices? The "Documentation" page comes close...I now know it talks over HTTP, but...what? I don't even know. It still surprises me that so many sites fail to clearly articulate a) what they do, and b) why I should be interesting in what they do. IMO it smacks of egocentrism and arrogance.