These items have to do with various points in the webkit rendering process. One trouble with benchmarking in a browser is that you're at the mercy of the browser's rendering engine. Fortunately, webkit is fairly fast, but its by no means a guarantee that its the best or fastest.
From memory, if I get these right:
docload: the main document is fully loaded (not including all subresources)
paint: the time to the first paint of the page
total: time at which everything is loaded and the pending queue of resources to be fetched is zero