Remote code execution
Also known as RCE
A vulnerability allowing an attacker to run their own commands on a system across the network.
RCE is the most serious class of vulnerability, because it hands the attacker direct control rather than access to a subset of data. On an internet-facing system it is an emergency.
When one is disclosed in a product you expose, the response is measured in hours. Mass exploitation of internet-facing RCE typically begins within days of a public exploit appearing.
Where this comes up
Remote code execution sits inside our penetration testing work. If you are trying to work out what this means for your own environment rather than in the abstract, that is the page worth reading next, and a short call will get you a straight answer faster than either.