Ancestry Informative Marker
From SNPedia
Ancestry Informative Marker (AIM)s are the subset of genetic markers that differ in allele frequencies across different populations of the world. Most variations are shared among populations, so for most loci the most common allele is the same in each population. AIMs may be used to categorize individuals into populations sharing similar markers and perhaps phenotypes (such as self-declared ethnicity)
This article
and these
This page appears to identify ~300 snps which can distinguish european ancestry http://genepath.med.harvard.edu/~reich/EUROSNP.genomeorder.frequencies.txt
