A term used when a locomotive previously in commercial service or storage has been returned to operational condition, usually in an original or otherwise heritage colour scheme. Many commercial locomotives that enter preservation require some degree of work to bring the locomotive up to a reliable operational condition. Locomotives that have been run down or in long term storage, perhaps with missing parts typically require a lot of work to be returned to service.
This term is also used when stored/retired locomotives have been preserved and made into static displays, typically with a fresh coat of paint and an overall clean.
Example: The NSWRTM restored 4001 to operational condition.