This vocabulary term refers back to blogging. Every time you post a new article in your blog, someone is able to comment on it. In fact you should invite the comments. The more people comment, the more active your blog will be because comments show new readers that your blog is actually worth reading.
However, there's a drawback to blog comments, and they are know as "comment spam." This is when a bot (there's that nasty bot again) or some person finds your blog and posts a useless comment unrelated to your article.
Let's say you just posted an article about the latest Tacori designs. "Comment spam" would be someone who then inserts a comment saying "That's a great article, I sell Tacori rings at www.mytacori.com." Obviously that type of comment is promoting some other website.
Another type of spam is when someone simply posts "Thanks for the info. John Smith, www.johnsmith.com." This type of spam is intended to trick people to click from your blog to their website.
All comment forms should have a CAPTCHA to prevent bot comment spamming. But you should also review and delete comments if you find them to be useless.