What’s a Poison Pill? Key Terms in Musk-Twitter Fight: QuickTake

Elon Musk is trying to take control of Twitter Inc., an effort Twitter is resisting. Exactly why Musk, the chief executive officer of Tesla Inc. and the world’s richest man, is fighting to buy the social media platform and take it private isn’t entirely clear, although he has long chafed at what he sees as excessive limits on expression on the social media platform. Also unclear to many: the blizzard of financial terms being thrown around, with “poison pill” perhaps the most prominent. Here’s a guide.

Schedule 13D

The U.S. Securities and Exchange Commission has rules requiring investors who are ...