Also known as the UcsdPsystem.
UCSD-P code (or simply UCSD-P) was a virtual machine used as a foundation for such languages as UCSD Pascal and DigitalResearch C-BASIC (CeeBasic).
This allowed the UCSD-P runtime "engine" to be implemented on the CPU & OS of choice, and take code written on some other machine (already compiled) and run the "MachineCode" on the new target without change.
One might say it allowed "WriteOnceRunAnywhere" -- or something like that.
See also JavaVirtualMachine for conceptual comparison/contrast.
See VirtualMachine