The term "haplotype" is a contraction of the term "haploid genotype".  In genetics, a haplotype is a combination of markers (technically called alleles) at multiple locations on a single chromosome.  Many genetic testing companies use the term "haplotype" to refer to an individual collection of short tandem repeat allele mutations (STRs) within a genetic segment, while using the term "haplogroup" to refer to the single nucleotide polymorphism mutations (SNPs) which determine the clade to which a collection of haplotypes belong.  To put this into layman terms, a haplotype is an individual's set of values for the markers that he has had tested.  If two individuals match exactly on all of the markers they have had tested, they are said to share the same haplotype and to be related.  The degree of relatedness can be predicted based on the number of markers that have been tested.  The more markers tested and compared, the better and more accurate the prediction.