What is "o-code"

O-code is an intermediate language emitted by the BCPL compiler. It is then compiled into the machine code for the computer which is intended to run the program. This method of compiling allowed the original BCPL compiler to be ported to new machines very easily and as a result it became widespread. The idea has since been used by many more recent compilers. However most of them interpret their equivalent of O-code on a virtual machine rather than compiling it as was originally the case.