The US military refers to this as TDY or Temporary Duty.
It is colloquially referred to as Temporary Duty Yonder, but the General Service Administration's Acronym Dictionary defines it as Temporary Duty.:
TDY: Temporary Duty
The pay is referred to as Temporary Duty Allowance in the GSA's Federal Travel Regulations.:
Chapter 301—Temporary Duty (TDY) Travel Allowances