In short it just means it installs the exact same packages every time. If you write `apt install something` without an explicit version you may get a newer vers

In short it just means it installs the exact same packages every time. If you write `apt install something` without an explicit version you may get a newer version depending on how recently you've updated your package manager. Our build server got burned by this because we wrote the line `apt update` within a Docker image. We did this at the time to get the most recent version of a package. Ideally we should have locked the version there, but we weren't really thinking of it until half a year later all our builds started failing. The package inadvertently updated and had breaking changes in it. With apt-lock you don't need to manually specify, you can just install once and then every reinstall will be the same (such as in a Docker image, or a new member joins your team and you're setting up their machine).