What you say? Damn Interesting describes it as;
Baader-Meinhof is the phenomenon where one happens upon some obscure piece of information– often an unfamiliar word or name– and soon afterwards encounters the same subject again, often repeatedly. Anytime the phrase “That’s so weird, I just heard about that the other day” would be appropriate, the utterer is hip-deep in Baader-Meinhof.
I just happened to see the term used yesterday, and then today I saw it as one of the Six Random Links on David Gagne’s blog.