Yeah, Negative SEO refers to "black hat" tactics witch attack anothers website. The easiest and most common negative SEO is actually fake bad business reviews. If you own a restaurant, and you go online to Yoast and give bad reviews online that are not true, that can be negative SEO.
Also bad backlinks, and some orphan pages can be negative SEO. The most referenced negative SEO was done in America by fan of the Democrat party in the early 2000's. Hundreds of SEO guys teamed up to create links to a picture of George Bush's face and tied the Anchor text to the word "failure." For the longest time you could type "failure" in Google and get the presidents face. Google finally manually removed that SERP.
Example of Negative SEO