Glossary

A separate line of work inside a repository. You experiment on a branch so main keeps working while you break things.

Turning your source code into the files that actually run or ship: bundling, compiling, optimizing. If deploys fail, the build log is where you look first.

Automation that builds and tests every change (CI) and ships the ones that pass (CD). Robots that judge your commits before your users have to.

Downloading a full copy of a repository, history included, onto your machine. Not the same as downloading a zip: a clone stays connected to its remote.

A saved snapshot of your changes with a message explaining why. Small, frequent commits are the cheapest insurance in software.

A running, isolated box with your app and everything it needs inside. Kill it, restart it, run five of them; the box is disposable, the image is not.

Putting your built app onto a server or hosting platform where other people can reach it. Localhost does not count.

The internet's address book: it turns a domain name into the IP address of a server. Changes take time to spread because answers get cached.

A named value handed to your app from outside the code, like an API key or a database URL. Different machines set different values, which is the whole point.

The frozen blueprint a container starts from: code, runtime, and dependencies in fixed layers. Containers are instances of an image, like processes are instances of a program.

Your own machine, talking to itself over the network. Anything running on localhost is invisible to the rest of the internet, which is both the feature and the problem.

Git asking a human to decide between two competing edits to the same lines. Annoying, normal, and fixable; it is a question, not an error.

A numbered door on a machine where a program listens for network traffic. Port 3000 on your laptop and port 3000 in a container are different doors until you map them.

A proposal to merge one branch into another, with a diff your teammates can review and comment on before anything lands.

A copy of your repository that lives somewhere else, usually GitHub or GitLab. Push sends your commits there; pull brings new ones back.

A project folder that Git tracks, including its entire change history. The .git directory inside is the part doing the remembering.

Any value that grants access: API keys, tokens, database passwords. Secrets live in environment variables or a secrets manager, never in the repository.

Storage that lives outside a container so data survives when the container is deleted. Databases in Docker without volumes are how you lose a weekend.