The purpose of this book is to providetelecomunications and digital media professionals with a collection of must-know term and concepts that are likely to pop up in their daily converstions or appear in news articles or informationl media that addreass ourincreasingly technologicalworld. It is also intended for anyone who simply wants to know more of what makes today's technological world go around. The use of "essential" in the title is not accidental.