In the context of computer and information sciences, an ontology defines a set of representational primitives with which to model a domain of knowledge or discourse. The Gene Ontology for example provides a controlled vocabulary to describe gene and gene product attributes in any organism.

Open Reading Frame a series of codons beginning with a start codon and ending with a stop codon, without any internal stop codons.

A differentiated structure within a cell, such as a chloroplast, mitochondrion or vacuole, which performs a specific function.

Orthologous are homologous sequences that have been separated by a speciation event. A gene that exists in a particular species that then diverges into two separate species, will be present in two copies afterwards. These copies are called orthologues and will typically have the same or a similar function.