Googlebot is Google's crawler (also known as a spider or robot) which traverses the web, viewing and saving pages for Google's search index.
Gray Hat SEO
Considered the middle ground between white hat and black hat SEO, gray hat SEO tactics are those that aren't explicitly defined as bad by search engines. Basically, if search engine guidelines don't state their position on a specific SEO technique, it may be considered gray hat.
Often, gray hat techniques are considered to not be aligned with the 'spirit' of the search engine guidelines, even if they aren't clearly defined as bad. For this reason, it is often best to avoid gray hat SEO techniques, but many people use their own judgment to categorize gray hat methods into either white hat or black hat categories.