Scrum is a part of Agile development. Looks like if Microsoft does buy Yahoo! they will also benefit from this practice.
Here's the skinny:
Lessons from a Yahoo Scrum Rollout: "The easiest way to describe it is that [software is developed in] small groups, which means small cycles and incremental [changes], which means that you release pieces of software rather than the typical big bang. Agile is the web describing the commonality between these things, which is very values driven, and Scrum is one of the methods. Scrum is a very lightweight framework in which you can adapt--and it's not just confined to software."
The article is long but very thorough.
