Often when people talk about negative SEO tactics, they’re talking about using extremely spammy links pointing to a competitor in an attempt to get the competitor’s page or site penalized. And yes, this actually happens...I have 2 clients in...
Spam is content / techniques generated only for search engines and not humans in an attempt to inflate ranking. Intent / targeting is key. Look for? Page level - doing things useless for end-users. Link-level: in & out links. Deceiving...
Spam more about intent of technique and the extent a technique is used, rather than being a specific technique. Where is the fine line? Varies by industry. Is a user comfortable with the user experience of a site (excessive links, nonsensical...