nt is a nucleotide sequence database composite made by NCBI. It
contains all GenBank/EMBL/DDBJ sequences (but no EST, STS, GSS, or
phase 0-2 HTG sequences) and nucleotide sequences from RefSeq and PDB.
nt (also called nr or nr_na) is the default database for BLAST at NCBI.
Despite its name, nt is not non-redundant but rather non-identical.
At CSC nt is available for BLAST searches.