The act of discussing someone or something online without using their name or by using an alternate name, so as to avoid giving them attention or receiving backlash from their followers, supporters, fans, etc. The phrase refers to Voldemort, the primary antagonist in the Harry Potter series, in which his name is taboo and many characters avoid saying it for various reasons, often by instead calling him "He-Who-Must-Not-Be-Named." Voldemorting is the same as hiding what you're talking about in plain sight. These people talking about Twitter with names like "birdsite" and "birdworld" are Voldemorting.