Shelf life was the length of time a chemical could remain potent while not in use. A product whose shelf life had ended was said to be expired.
Gronerium compound 3983 had a shelf life that exceeded ten standard years without its potency diminishing appreciably. This information was available on the USS Enterprise-D's computer database. (TNG-R: "Night Terrors", okudagram)
In 2377, Chellick declined Gar's offer to sell Hospital Ship 4-2 more cytogenics, claiming the last shipment consisted of expired lots and diluted samples. (VOY: "Critical Care")