“Gray Hat SEO” is not a phrase that can be defined easily.
I find Search engine optimization always depends on the tricks rather than its procedure. Basically there are 3 Methods of Search engine optimization.
1.White hat SEO
2.Black hat SEO
3.Gray hat SEO : Gray methods that are not totally Prohibited to use by Search engine, but also not allowed as legal [procedure. As they have said already it’s a combination of those other two SEO methods. This is because the guidelines in the search engines are not clear enough.
So more to say elaborately Gray hat method is the practice of tactics/techniques which remain unclear by published material coming out of Google published guidelines.
Grey hat technique contains such as:
• Purchasing old domains
• Duplicating content
• Buying link
• Social media automation and purchasing followers
It depends on the purpose for which techniques are using to rank your site. A proper understanding of Gray Hat method is really important because you can improve your site’s ranking without negative consequences, or it can cost you thousands in lost traffic.