In bioinformatics, k-mers are substrings of length k {\displaystyle k} contained within a biological sequence. Primarily used within the context of computational genomics and sequence analysis, in which k-mers are composed of nucleotides (i.e. A, T, G, and C), k-mers are capitalized upon to assemble DNA sequences, improve heterologous gene expression, identify species in metagenomic samples, and create attenuated vaccines. Usually, the term k-mer refers to all of a sequence's subsequences of length k {\displaystyle k} , such that the sequence AGAT would have four monomers (A, G, A, and T), three 2-mers (AG, GA, AT), two 3-mers (AGA and GAT) and one 4-mer (AGAT). More generally, a sequence of length L {\displaystyle L} will have L − k + 1 {\displaystyle L-k+1} k-mers and n k {\displaystyle n^{k}} total possible k-mers, where n {\displaystyle n} is number of possible monomers (e.g. four in the case of DNA). Source: Wikipedia (en)