An artefact needs somewhere to run. A container brings its surroundings with it. Serverless hands the surroundings to someone else.
Container
Also called Docker container, Container image
A way to package a program with all the files it needs and run it as an isolated process, so that it behaves the same on your laptop and on a server.
It makes "works on my machine" a smaller problem, because the machine's contents travel with the program. It also gives an agent a place to run commands where a mistake is more likely to stay inside.
Say it to your agent
“Write a Dockerfile: pin the base image by digest, copy only what the app needs, and run as a non-root user. Build it in CI, and run it here with docker run before you tell me it works.”