An ORF (Open Reading Frame) corresponds to a stretch of DNA that could potentially be translated into a polypeptide or RNA; i.e., it begins with an ATG "start" codon and terminates with one of the 3 "stop" codons. For an ORF to be considered as a good candidate for coding a bona fide cellular protein, a minimum size requirement is often set, e.g., many of the systematic sequencing groups define an ORF as a stretch of DNA that would code for a protein of 100 amino acids or more. An ORF is not usually considered equivalent to a gene or locus until there has been shown to be a phenotype associated with a mutation in the ORF, and/or an mRNA transcript or a gene product generated from the ORF's DNA has been detected. See ORF naming conventions for how ORFs are named in Saccharomyces cerevisiae.

This definition is in context to Yeast Genome. See more contextual defintions for ORF.