Selective disclosure is the improper sharing of material non-public information with a favored subset — analysts, big investors — before the broad market, the practice Reg FD was written to prohibit. It can happen inadvertently in a hallway conversation, a conference, or a sloppy investor meeting, creating serious legal and reputational exposure. Preventing it is why IR tightly controls executive interactions with the Street and trains spokespeople on what can and can't be said.