Genotyping refers to the process of comparing genetic markers (i.e., alleles) taken from a large number of members of the same species to obtain a more complete picture of that species's phylogeny. For example, an allelic marker may be represented by an SNP or a microsatellite.
The inheritance of markers offers us something of a genetic roadmap to human ancestry on the scale of populations, which is why there are large-scale projects in place (such as National Geographic's Genographic Project) that aim to genotype members from each population on Earth in the hope of constructing such a roadmap.
