There are five different blast programs, which can be distinguished by the type of the query sequence (DNA or protein) and the type of the subject database:
BLASTP compares an amino acid query sequence against a protein sequence database;
BLASTN compares a nucleotide query sequence against a nucleotide sequence database;
BLASTX compares the six-frame conceptual translation products of a nucleotide query sequence (both strands) against a protein sequence database;
TBLASTN compares a protein query sequence against a nucleotide sequence database dynamically translated in all six reading frames (both strands).
TBLASTX compares the six-frame translations of a nucleotide query sequence against the six-frame translations of a nucleotide sequence database.