Hi Sarah,
Basically, MBA accreditation is exactly like the accreditation most degree courses require before they can be officially considered a proper qualification. So jsut as a BA, an MA, A PhD in any subject must be officially accredited (usually by an external examining body of some sort), and standards governed. This allows both students and employers to know the true value of the qualifications on offer, so it's very much to your short and long-term advantage to make sure the place you apply to is properly accredited.
There are many different governing bodies which offer accreditation to schools and programmes which they consider meet their standards; some operate nationally, some internationally, whilst others within more local boundaries. The AACSB (Association to Advance Collegiate Schools of Business), operates world-wide, whilst there are six accrediting bodies in the US. In Europe, the main ones are AMBA (Association of MBAs), EQUIS (European Quality Improvement System, which also covers some Asian schools), and FIBAA (Foundation for International Business Administration Accreditation).
You can check out some of their official websites for further clarification of the standards institutions are required to meet before they are officially accredited. See, for example:
http://www.mbaworld.com/page/welcome/index.htmlhttp://www.efmd.org/html/home.asp (look for the section on accreditation)
and
http://www.fibaa.de/engl/home.htmBest,
lukeh