1) The length of a nucleotide sequence that is repeated in a tandem cluster.

2) Multiple copies of the same base sequence on a chromosome; used as markers in physical mapping.

3) A tandem repeat is a sequence of two or more DNA base pairs that is repeated in such a way that the repeats lie adjacent to each other on the chromosome. Tandem repeats are generally associated with non-coding DNA. In some instances, the number of times the DNA sequence is repeated is variable. Such variable tandem repeats are used in DNA fingerprinting procedures.