Meta tags are snippets of text that describe a page's content; the meta tags don't appear on the page itself, but only in the page's code. ... The “meta” stands for “metadata,” which is the kind of data these tags provide – data about the data on your page.
The rel=canonical element, often called the “canonical link”, is an HTML element that helps webmasters prevent duplicate content issues. It does this by specifying the “canonical URL”, the “preferred” version of a web page – the original source, even. Using it well improves a site's SEO.