When a hostile takeover bid is announced, investment bankers and corporate lawyers almost immediately start throwing jargon around. Here are some definitions that corporate executives involved in a takeover battle may find useful: the real meaning of a "poison pill", the high-stakes "pac-man" defence or the difference between a "13-g" Securities and Exchange Commission filing and a "13-d". Then there is the impact of the Unocal and Revlon court decision on US merger law.

Poison Pill : This term, coined in the 1980s by New York merger lawyer Martin Lipton, involves issuing new stock to existing shareholders in the event that a bidder takes control of a large stake in the company. The effect of the poison pill is to dilute the bidder's holding, making the acquisition much more expensive. Although poison pills are rarely triggered, they serve as strong deterrents to hostile bids. But many shareholder groups have in recent years pressed companies to dismantle their "pills".