Dictionary:

locum tenens

  (lō'kəm' tē'nĕnz', tĕn'ənz)

A person, especially a physician or cleric, who substitutes temporarily for another.

[Medieval Latin locum tenēns : Latin locum, accusative of locus, place + Latin tenēns, present participle of tenēre, to hold.]

A replacement for an absent veterinarian whose responsibility is to provide exactly the same services and at the same standard as those provided by the absentee.

One holding a place

The noun has one meaning:

Meaning #1: someone (physician or clergyman) who substitutes temporarily for another member of the same profession
  Synonym: locum