The cellular production of the protein encoded by a particular gene. The process includes transcription of DNA, processing of the resulting mRNA product and its translation into an active protein.
A recombinant gene inserted into a host cell by means of a vector is said to be expressed if the synthesis of the encoded protein can be demonstrated.
Source: PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 153 (https://doi.org/10.1351/pac199264010143)