Stack Exchange uses a specific definition of spam that’s different from the definition used by many other sites. It’s most concisely detailed in the flag dialog:
Exists only to promote a product or service, does not disclose the author’s affiliation.
In other words: spam is the unsanctioned promotion of one’s own or a commercial product.
There’s an FAQ post on the topic of what spam is on Meta Stack Exchange, if you’d like the full story.
That means this is spam:
Who are they who believe that reason to look into anything that writes Malegenix so poorly? Do you have to not appear adventurous? It is also rewarding when you discover a Malegenix. This can be sized to fit. They were a lot more active after this. I can express this touching on Malegenix. That is dirty. It seems very interesting. Isn’t this exactly the function of Malegenix today?
Visit here <spammy link>
(That’s a real post, by the way.)
This is also spam, if the blog belongs to the post’s author:
Visit this awesome blog (link) to find the answer!
However, this is not:
To fix your problem, you should foo your bar and pass your baz to quux.
I wrote about this in more detail on my blog (link).
That post discloses the fact that the blog is the author’s, so it’s okay.
This isn’t spam either:
delete me delete me delete me delete me delete me
If you come across something along those lines, it’s most likely self-vandalism, which is where a post’s author has removed a post’s content in an effort to delete it. That’s not something Stack Exchange allows, but it’s not spam.
As always, use your best judgment, and ask if you’re not sure.