Once upon a time, much like search engine submission, meta tags (in particular, the meta keywords tag) were an important part of the SEO process. You would include the keywords you wanted your site to rank for and when users typed in those terms, your page could come up in a query. This process was quickly spammed to death, and eventually dropped by all the major engines as an important ranking signal.
It is true that other tags, namely the title tag (not stictly a meta tag, but often grouped with them) and meta description tag (coveredpreviously in this guide), are of critical importance to SEO best practices. Additionally, the meta robots tag is an important tool for controlling spider access. However, SEO is not "all about meta tags", at least, not anymore.
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