@bammerlaan it's basically someone who replies excessively or in an unhelpful way, often without understanding what the original poster was talking about. I think it's usually about unwanted/bad advice, but I also use the term for annoying commenters in general.
I didn't really understand it until being subjected to it a few times. I like to post about shows and movies I like and I have had to deal with people showing up and explaining the plot/characters to me in the replies, even though I never asked. One time I posted some screenshots from a show I had watched, included the series name and plot description, and a guy tried to argue with me that I was "mistaken" and that I was wrong about what show I was watching... I wasn't lol. I had no idea how to even respond to that so I just blocked him.
I'm filtering mastodon dot social and that helps cut down on unwanted replies and also spam