Here I found a new terminology first time:
Looks like a spam seed is a post, which "is designed to allow spammers to post questions so it looks legitimate".
What does this mean? Maybe it is some type of a spamfilter poisoning?
The description is pretty much spot on. In that context a "spam seed" is a post disguised as an actual question, but which only serves the purpose of being able to post a spammy answer after some time. And that answer may just pass as an actual answer for a longer amount of time than desired. It passes spam defences in as much that the question itself isn't really spam.
The quality of such seeds however is usually so terrible that it's not much of a disguise. In that sense I wonder if any poisoning is really taking place. False positives on actual crap perhaps aren't really that big of a deal.
Yup, it's part of a coordinated campaign to spam file recovery tools to Stack Overflow, Super User, Server Fault, and other sites on the network: meta.stackoverflow.com/a/269868/19679 . They've been getting progressively more creative with their spam, now seeding questions with one account and answering with another. The real problem is that reviewers are usually approving their spam now, so I have to sweep through every few days and remove the spam that made it through.
Spam seeds are a somewhat slang term (just now added to the glossary by me), but it describes (usually softball) questions with the only purpose to attract spam or to allow spam to be posted as an answer.