“White hat SEO” refers to SEO techniques, best practices, and strategies that abide by search engine rule, its primary focus to provide more value to people.
“Black hat SEO” refers to techniques and strategies that attempt to spam/fool search engines. While black hat SEO can work, it puts websites at tremendous risk of being penalized and/or de-indexed (removed from search results) and has ethical implications.
Penalized websites have bankrupted businesses. It’s just another reason to be very careful when choosing an SEO expert or agency.