Black Hat and Gray Hat Seo Tactics?

Black Hat Seo Tactics

Keyword stuffing

Overusing keywords in comment tags, alt tags, and meta tags

Doorway or gateway pages

Link farms: pages with unrelated links solely for the purpose of creating more links to target pages

Spamming forums, blogs, and other social media sites with links (search engines might not penalize sites for this, but it's considered unethical)

Cloaking: Presenting different information to the search engines through Meta tags/descriptions.

Hidden Text: When text/keywords are the same color as the background. Search engines see it; readers do not.

Gray hat SEO Tactics

Having a keyword density that's high enough to sound unnatural but not at the level of black hat keyword stuffing

Publishing duplicate content at different sites

Link building where relevance is less important

Planned three-way linking
Using paid links

Automated Social Media: Some websites send users an automatic message when connecting via social media. Although search engines will not dock a company for this, it’s considered more annoying than anything.