White hat SEO is the process of using "ethical" techniques to help a website rank high in search engine result pages. These techniques are recommended by the search engines themselves, as they help the search engines also, and include things like: proper <title> tags, appropriate meta descriptions, <h1> tags, alt tags for images, etc.
Grey hat SEO techniques fall in the region between white hat SEO and those areas that are known to be wrong -- black hat SEO
. Some people call grey hat SEO techniques to be "aggressive" SEO. I've used it at times for pages that I wanted to show up higher in search engine results for phrases that are more competitive. They're techniques that range from ethical to non-ethical, depending on the greyness.
Google and other search engines will not tell you where a firm line lies, or if you cross a line what specifically will happen. However, you or your SEO provider take a risk if you cross into the grey area as your webpage and/or website URL may be penalized.
Grey hat SEO techniques and tactics may include:
- Keyword or phrase stuffing
- Meta-tag keyword or phrase stuffing
- Paid links on other sites for the purpose of increasing your link popularity
- Planning multi-way linking between sites