Grey-hat SEO: Breaking a rule or two, usually when you know how to use black-hat tools properly and efficiently, makes use of SE (search engine) courtesy and human emulation settings, uses proxies, etc. Just as effective.
Black-hat SEO: Unethical SEO practises, unrelated, spammy backlinks, mass submission (low delay settings if any), uses proxies, fast automation tools. Also effective, short-term unless you really know what you're doing. Can easily cause Google penalties in the wrong hands.