Haplogroups:

Definition: Haplogroups characterize the early migrations of
specific population groups and, therefore, can potentially be used to connect
your distant ancestry with a particular geographical region. For the purpose of
genetic genealogy, a haplogroup can be defined as all of the descendants of a
single individual who first showed a particular single nucleotide polymorphism,
or SNP. An SNP is a point on the DNA where a single base changes (e.g. from A to
G), which occurs so infrequently that it can be considered unique. This SNP
change is then passed down faithfully through generations of the family, and can
thus be used to define broad genetic populations. Individuals with the same
genetic SNP mutation or "marker" can be linked back to the population where the
marker first made an appearance.