It is a post that does not add much, if any, context, information, opinion, or otherwise original content to the post it links to. It is essentially a blog post that say "Hey! I found this cool post here! You should read it!" It is considered "spam" because the post it links to is inherently more valuable than the blog post itself; if the blog post added valuable content or insight to the linked article, it would not be considered blogspam.
Well I'm going to have to disagree with you. The NYT article had a lot of words in it I didn't care about. I only wanted to share the story about the cheeseburger. All the words around it made things more complicated and obscured the story about the cheeseburger. The brevity was quite valuable to me.It is considered "spam" because the post it links to is inherently more valuable than the blog post itself