Glossary — D
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Database
A persistent, structured store for an application’s data. Comes in two main families: relational (data in tables with strict columns, queried with SQL — e.g. Postgres, MySQL) and non-relational / NoSQL (more flexible structures — e.g. MongoDB, DynamoDB, Firestore). Most web apps use a relational database.
See also: What is a database?, Postgres, SQL
Debug
The process of finding and fixing a bug. Practically: reading logs, adding console.log statements, stepping through code, asking Claude to explain what’s wrong, or staring at the screen until something clicks. The amount of time spent debugging often exceeds the time spent writing the code in the first place.
See also: Bug
Dependency
A library or package that your project relies on. Listed in package.json. When you npm install, all of them (and their dependencies, and their dependencies) get downloaded into node_modules/. A modern React project typically has hundreds or thousands of transitive dependencies.
Deploy
Take a built version of your app and put it somewhere users can reach it. “Deploying to production” means making the new code live on the actual website. Modern hosting (Vercel, Netlify) deploys automatically when you push to your main Git branch.
See also: Deploy a Next.js app to Vercel, CD
Diff
A representation of what changed between two versions of a file (or set of files). Shown as a list of removed lines (red, marked -) and added lines (green, marked +). Git diff, GitHub PR diffs, and Claude’s edit previews all use the same format.
See also: Git basics
DNS (Domain Name System)
The internet’s phone book. Translates human-readable names like stmarkbible.com into numeric IP addresses like 76.76.21.21. Without DNS you’d need to memorize every server’s IP. DNS records propagate slowly — a change can take minutes to days to be seen everywhere.
See also: Domains and DNS
Docker
A tool for packaging an application along with its entire runtime environment (OS libraries, system packages, config) into a portable “container.” If it runs in the container on your laptop, it’ll run identically on any server with Docker. Big in the broader software industry; less central to Vercel-style web hosting since the platform handles environments for you.
See also: Containers & Docker
DOM (Document Object Model)
The live tree of HTML elements that a browser builds when it loads a page. JavaScript can read it (document.getElementById(...)), change it (element.textContent = "Hi"), or rebuild parts of it. React works by computing what the DOM should look like and updating only the parts that changed.
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