This are the most well known type of Grayware, there are what we usually call pop-ups that appear on those sketchy web pages. This ads usually promote more malware or scams, they are created to make money since everything you see promoted there it's because someone payed money for that promotion, the more clicks they make the more money they make. while anoying they are not very harmful.

Spyware is a type of malicious program specifically prepared to illegally spy on the victims system and collect data such as visited websites and general infos about the user or the machine. sometimes even trusted operating systems have spyware installed in them by default. data collect with this method will usually be sold to companies to target the user with better ads