The Baader-Meinhof Phenomenon, also known as the frequency illusion, is a cognitive bias or psychological phenomenon in which something that has recently come to your attention suddenly seems to appear everywhere. In other words, after you notice or learn about a particular thing or concept, you start seeing it more frequently in your day-to-day life.

This phenomenon can occur because your brain becomes more attuned to the newly noticed item or concept, and as a result, you start noticing it more often. It's not that the thing or concept has suddenly become more prevalent; rather, your increased awareness makes it seem that way!