Short for "Commercial Stable Image Platform", it is a specification aimed at businesses for OEMs that guarantees parts supplied in particular configurations for a period of 15 months will all be identical, something that Intel has already been doing for some years. This is in response to increasing industry awareness of alternatives to Intel and the rate of adoption for AMD processors in the workplace increasing. The current specification puts the Athlon64 X2, Athlon64, and Turion64 in partnership with certain manufacturers only, such as nVidia, ATI, ASUS, ECS, Gigabyte, MSI, Broadcom and Atheros.
What makes this important and interesting? When you deal with volume manufacturing, a huge amount of your time is devoted to the creation and deployment of images for provided software, and resolving any incompatibilities that may crop up with various hardware configurations. One of the reasons many businesses are standoffish towards AMD is the fear of having a huge number of computers with compatibility problems that can't be worked around. This resolves that problem, and puts businesses at ease knowing that they will get a solid, stable, tested product that is guaranteed to support what it says it will. This is a good thing, as it doesn't restrict end-users in any way and promotes the adoption of AMD into the businesses environment, a place where it is lagging behind Intel to a large degree.