What is the SEO Recommended canonical category of products?

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What is the SEO Recommended canonical category of products?

"canonical category of products??"

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.