1) A reading frame in a sequence of nucleotides in DNA that contains no termination codons and so can potentially translate as a polypeptide chain.

2) A reading frame that does not contain a nucleotide triplet which stops translation before formation of a complete polypeptide -- abbreviation ORF.

3) An open reading frame is a portion of a DNA molecule that, when translated into amino acids, contains no stop codons. The genetic code reads DNA sequences in groups of three base pairs, which means that a double-stranded DNA molecule can read in any of six possible reading frames--three in the forward direction and three in the reverse. A long open reading frame is likely part of a gene.