It’s used fairly often in the US national lab community (Not just among physicists). I think the point is that the physicists were among the very early adopter

It’s used fairly often in the US national lab community (Not just among physicists). I think the point is that the physicists were among the very early adopters of computing systems. I’m not sure about the history of the term “code” used this way, but it might literally predate compiled software since Ulam and von Neumann invented the Monte Carlo method in 1948 during the Manhattan Project. Personally I think it just sounds outdated now, but it’s pretty common to hear people call their software “a hydrodynamics code” or “a molecular dynamics code”