remote code execution
when an outsider can make a computer run their own commands
Remote code execution is the most serious kind of software flaw. It lets an attacker, from somewhere else on a network, run commands of their choosing on a machine. They do not need to sit at the machine or hold an account on it. Whatever that machine can reach, the attacker can now try to reach too.
Think of it as
Like a stranger who can phone a factory and have the machines follow their instructions.