Is there anything in any airport called a "warm apron"?
A warm up apron is a portion of the airfield close to the runway entry, where the engine can be warmed up before taking off. It seems to be more frequently used in military documentation.

There are such aprons at Cairns Army Airfield:


Source

Found in FAA regulations, e.g. AC 150/5340-30:


  PAPI LHAs must not be located closer than 50 ft from a crossing
  runway, taxiway, or warm-up apron or within the ILS critical area.


But also in other not regulatory documents, here for synonymous of hardstand:


  ... construction of the RMP test section and warm-up apron (hardstand)
  at the east end of Runway 04-22. The RMP warm-up apron was
  successfully constructed and has been opened for traffic since October
  1992.


Source: Design, Construction and Performance of Resin Modified Pavement at Fort Campbell Army Airfield, Kentucky

A vintage post-card:


Source: eBay