A kmer or k-mer is a short DNA sequence consisting of a fixed number (K) of bases. The value of k is usually divisible by 4 so that a kmer can fit compactly into a basevector object. Typical values include 12, 20, 24, 36, and 48; kmers of these sizes are referred to as 12-mers, 20-mers, and so forth.
Kmers are essential to pre-processing of reads and contigs. A typical procedure is to cut a contig into a series of overlapping kmers; each kmer overlaps with its neighbors in all but one base as they step through the sequence. This is how lookup tables are generated.
A mutmer is a kmer of variable ("mutable") length K. Certain algorithms involving kmers have been adapted to use mutmers within a range of lengths.