White hat SEO basically means that to do SEO according to Google norms. Not to use restricted techniques or spamming in the name of optimization.
White SEO is a type of SEO strategy that abides to the rules of a search engine like Google, Bing, and Yahoo. The opposite for this one is Blackhat SEO, which mostly uses dirty tricks like bots and cloaking. These do not abide to Google's rules.
In SEO terminology, white hat SEO refers to optimization strategies, techniques and tactics that focus on a human audience. This is compared to black hat tactics which are the strategies that are banned by google because they take advantage of the system, are suspicious or fraudulent.