What is permissive tdy?

Some articles on permissive tdy:

Leave (U.S. Military) - Types of Leave
... return to duty for an extended period of time, permissive TDY (Temporary Duty), which is non-chargeable and is only used while traveling between stations while using their leave for government related purposes ... Servicemembers using PTDY (Permissive TDY) are not charged while on leave but are also not granted travel pay ... Permissive TDY is typically used when PCSing (Permanent Change of Station) and can be granted to a service member when looking for a place to live ...