...but when I do, people laugh. If you are one of the folks that are prone to laughing at such a thing, here is what Scrum is:

What is Scrum?

Scrum is an iterative, incremental process for developing any product or managing any work. It produces a potentially shippable set of functionality at the end of every iteration. It's attributes are:

• Scrum is an agile process to manage and control development work.
• Scrum is a wrapper for existing engineering practices.
• Scrum is a team-based approach to iteratively, incrementally develop systems and products when requirements are rapidly changing.
• Scrum is a process that controls the chaos of conflicting interests and needs.
• Scrum is a way to improve communications and maximize co-operation.
• Scrum is a way to detect and cause the removal of anything that gets in the way of developing and delivering products.
• Scrum is a way to maximize productivity.
• Scrum is scalable from single projects to entire organizations. Scrum has controlled and organized development and implementation for multiple interrelated products and projects with over a thousand developers and implementers.
• Scrum is a way for everyone to feel good about their job, their contributions, and that they have done the very best they possibly could.

(from: http://www.controlchaos.com/about/)

A Certified ScrumMaster is simply a person who has been trained (and passed the training) by an accredited Scrum trainer.