Product Keywords vs Tags
The Edit Product form has two seemingly similar fields named Keywords and Tags.
Keywords
Keywords have multiple purposes. First, keywords will appear in the HTML meta field of the public product page. In other words, it is a search engine optimization (SEO) tool. Second, keywords influence the TitleLeaf search engine. Therefore, if you want a certain product to be included in TitleLeaf's search results for a certain term, add the term to the Keywords field. Third, Keyword data is distributed to third-party wholesalers/distributors (if requested) and is included in the ONIX feed.
Tags
Tags address a single need: to group products under specific terms without using the Subjects module. It is similar in functionality to Subjects but is hidden from visitors. This allows the publisher to create a page showing select titles without having the term appear in the Subjects hierarchy. It's useful for temporary promotions. Tag data is not distributed to third-party wholesalers/distributors and is not included in the ONIX feed.