FASTA

FASTA is a bare-bones flat-file format for DNA, RNA and protein sequence data. It's the most widely used & understood format for unannotated sequence, probably due in large part to its simplicity.

It can also be used to represent multiple alignments (see gapped FASTA format).

For details see e.g.

• Fasta format (Wikipedia)
• http://www.ebi.ac.uk/help/formats_frame.html