Merge PR #41 - Add definitions of frontend and server extensions

Author: mfisher87

03-vocabulary.md

@@ -4,12 +4,30 @@
 Extension
 : The end-user-installable delivery mechanism or container for {term}`plugins <plugin>`.
 An extension is a collection of 1 or more {term}`plugins <plugin>`.
+It's very common for {term}`frontend extensions <frontend extension>` and
+{term}`server extensions <server extension>` to be bundled together as one extension
+(in fact, we'll do that as part of this workshop).
 [See the official docs for more!](https://jupyterlab.readthedocs.io/en/stable/extension/extension_dev.html#overview-of-extensions)
 
 Core extension
 : JupyterLab is composed of modular {term}`extensions <extension>`.
 Core extensions are included with JupyterLab.
 
+Server extension
+: An extension which provides new functionality on the back-end.
+Unlike frontend extensions, server extensions have access to the computer JupyterLab is
+running on, for example to read files from disk.
+[See the official docs for more!](https://jupyter-server.readthedocs.io/en/stable/developers/extensions.html)
+
+Frontend extension
+: An extension which modifies the user interface and/or adds functionality that executes
+solely in the browser, and interacts with existing JupyterLab frontend components.
+This includes themes, UI elements, viewers, code editors, and more.
+They are built with [Lumino](https://lumino.readthedocs.io/en/latest/) and/or
+[React](https://react.dev/learn) components.
+Many frontend extensions are part of a larger extension with a
+{term}`server extension <server extension>` component.
+
 Plugin
 : The atomic building blocks of JupyterLab architecture and JupyterLab {term}`extensions <extension>`.
 Every extension includes >= 1 plugin.