1. The interval of geologic time equivalent to the chronostratigraphic unit ‘stage’. Ages are subdivisions of epochs and may themselves be subdivided into chrons. An age takes its name from the corresponding stage, so like the stage name it carries the suffix ‘-ian’ (or sometimes ‘-an’); the term ‘age’ is sometimes capitalized when used in this formal sense, e.g. ‘Oxfordian Age’.

2. An informal term to denote a time span marked by some specific feature, e.g. ‘Villafranchian mammalian age’.