White Hat SEO tactics and strategies are those optimization strategies, techniques and tactics that are considered acceptable and ethical by the search engines, especially by Google. These types of strategies focus on actual human audience, rather than just machine generated numbers. These strategies completely follows search engine rules and policies, hence the name, white hat, similar to the context white collar.
Black Hat SEO tactics and strategies, on the other hand, are those strategies that are considered unethical by search engines, i.e. especially by Google. These types of strategies do not focus on actual human audience but instead are just focused on improving their numbers, regardless of whether or not those numbers actually correspond to an audience.