The Baader Meinhof Phenomenon is a Cognitive Biase in which you notice a particular thing everywhere after noticing it somewhere.

A common example is buying a car and suddenyl seeing it everywhere.

Why is it called the Baader-Meinhof Phenomenon?

Kate Kershner has the following explanation in her What’s the Baader-Meinhof phenomenon? :

It all started in the comments section of a newspaper called the Minnesota St. Pauls Pioneer Press. During the 90s, one commenter talked about the Baader-Meinhof group, which was a West German terrorist organization, and within hours, he saw another reference to the group. Hence, the term was coined as the Baader-Meinhof phenomenon.