Locum
A locum is a person who temporarily fulfills the duties of another. For example, a locum physician is a physician who works in the place of the regular physician when that physician is absent, or when a hospital/practice is short-staffed. These professionals are still governed by their respective regulatory bodies, despite the transient nature of their positions.
The word locum is short for the Latin phrase locum tenens ("place holder", akin to the French lieutenant). The abbreviated form "locum" is common in Australia, Canada, Ireland, Malaysia, Singapore, New Zealand, South Africa and the United Kingdom; unlike in Latin its plural is locums. In the United States, the full length "locum tenens" (plural: locum tenentes) is preferred, though for some particular roles, alternative expressions (e.g., "substitute teacher") may be more commonly used.
In healthcare
In the UK, the NHS on average has 3,500 locum doctors working in hospitals on any given day, with another 17,000 locum general practitioners. Many of these locum hospital doctors are supplied by private agencies through a national framework agreement that the NHS holds with 51 private agencies. NHS figures show that approximately 80% of hospital locum positions are filled by agencies on this framework. The remaining 20% are filled by agencies working outside this agreement. Locum agencies are common reference points for doctors wishing to work in this market. According to a report published by Royal College of Surgeons NHS spent approximately £467 million on locum doctors through agencies in the year 2009/2010.