What are the difference between Chrome, Canary and Chromium?
- Your interpretation is correct
Canary is basically a (near) nightly release built from the current tip of tree of the Chrome repo. It's the bleeding edge of development and so you should expect crashes and bugs but it's the quickest way to test recent changes to chrome. (Aside from building ToT yourself)
Aside from Canary, there's also the Dev channel which is a slightly longer development release, usually about weekly, but still built from the bleeding edge tip-of-tree. Beta channel is a long running branch that's the upcoming release and is generally quite stable/bug free.
The order from "freshness" to "stable": Canary -> Dev -> Beta -> Stable
Chromium is the name of the open-source project from which Chrome is built. A Chromium build is basically equivalent to Chrome but doesn't include proprietary bits (Flash plugin, codecs, etc) or official Google branding (icons, etc).
Compatibility in terms of web-facing APIs between the different versions should be essentially the same except, of course, for intended upcoming changes. In general, changes that occur in Canary, Dev, and especially Beta, are intended to make it to Stable channel so it's a good idea to test your apps against Beta to make sure your app will continue to function as expected once the Beta is promoted to Stable. You can find upcoming changes to Web APIs at ChromeStatus
In Canary and Dev, you're more likely to run into unintentional bugs that creep in during development. If you'd like to help Chrome development you can file bugs for these at the Chromium bug tracker (use this for bugs you find in Stable/Beta channel too!)
In terms of performance, a hand-built Chromium will depend on who built it and with what flags. The performance between Canary/Dev/Beta/Stable should be comparable and indicative of the final stable release.