Add Bun glossary entry (#37814)

* feat: add Bun glossary doc

* fix: content changes

* Update files/en-us/glossary/bun/index.md

---------

Co-authored-by: Joshua Chen <sidachen2003@gmail.com>

files/en-us/glossary/bun/index.md

@@ -0,0 +1,21 @@
+---
+title: Bun
+slug: Glossary/Bun
+page-type: glossary-definition
+---
+
+{{GlossarySidebar}}
+
+**Bun** is a fast and modern {{Glossary("JavaScript")}} runtime environment designed to prioritize performance and developer tooling.
+
+Unlike [Node.js](https://nodejs.org/) and [Deno](https://deno.com/), Bun is built on Apple's [JavaScriptCore](https://trac.webkit.org/wiki/JavaScriptCore). Notable features of Bun include:
+
+- Drop-in Node.js replacement: almost all Node.js programs can run using Bun-equivalent commands.
+- State-of-the-art JavaScript execution speed in most real-world scenarios.
+- Native support for JavaScript syntax extensions like JSX and TypeScript.
+- Global cache for managing package installations to minimize disk usage.
+- Built-in bundler, transpiler, [Jest](https://jestjs.io/) compatible test-runner, package manager, and more built-in utilities that web developers may find useful.
+
+## See also
+
+- [Bun website](https://bun.sh/)