docs: add glossary of ambiguous terms to reference docs

docs/glossary.md

@@ -0,0 +1,75 @@
+(glossary)=
+
+# Glossary
+
+```{currentmodule} click
+```
+
+This glossary defines key terms as they are used throughout the
+Click documentation. It helps us be internally consistent in how
+we refer to concepts.
+
+```{glossary}
+
+Command Line Application
+    A program that is operated through a command-line interface
+    (CLI). A command line application accepts text commands,
+    options, and arguments typed into a terminal. Click is a
+    toolkit for building command line applications in Python.
+
+    Many command line applications provide multiple {term}`commands`,
+    each performing a different action. For example, `git` is a
+    command line application with commands like `git commit` and
+    `git push`.
+
+    See {doc}`quickstart` for getting started.
+
+Command Line Utility
+    A command line application designed to perform a specific,
+    focused task. The terms "command line application" and
+    "command line utility" are largely interchangeable, but
+    "utility" emphasizes a narrower, task-oriented purpose.
+
+    Examples of command line utilities include `black` (code
+    formatter), `pip` (package installer), and `flake8` (linter).
+
+Flag
+    An {term}`option` that takes no value. A flag is either
+    present or absent on the command line. Click implements
+    flags as boolean options using {func}`option` with
+    ``is_flag=True``.
+
+    A common pattern is the boolean flag pair, where ``--flag``
+    sets a value and ``--no-flag`` unsets it. This is
+    Click's default for boolean options.
+
+    See {ref}`option-boolean-flag` for details.
+
+Option
+    A named parameter passed to a {term}`command` on the command
+    line. Options are prefixed with dashes (``--verbose``,
+    ``-v``) and are defined with the {func}`option` decorator
+    or the {class}`Option` class.
+
+    Options can accept values (``--name Alice``), act as
+    {term}`flags <flag>` (``--verbose``), or count occurrences
+    (``-vvv``). Options are positional with respect to commands
+    but not positional with respect to other arguments on the
+    command line.
+
+    See {doc}`options` for the full reference.
+
+Terminal
+    A text-based interface for interacting with a computer. The
+    terminal (also called console, shell, or command prompt)
+    allows users to type commands and see output. When Click
+    runs, it reads input from and writes output to the terminal.
+
+    Click handles terminal interaction through utilities like
+    {func}`echo`, {func}`prompt`, and {func}`confirm`, which
+    adapt to the capabilities of the user's terminal, including
+    color support and Unicode rendering.
+
+    See {doc}`quickstart` for an introduction to using Click
+    from the terminal.
+```

docs/index.rst

@@ -118,6 +118,7 @@ General Reference
    command-line-reference
    unicode-support
    wincmd
+   glossary
 
 API Reference
 -------------------