feat(AEP-3): add AEP for glossary (aep-dev#73)

As a precursor to additional AEPs (e.g. resource types),
adding a glossary to ensure common terminology across
the AEP document.

This deviates slightly from google.aip.dev/0009. Most notably:

- Eliminates the concept of multiple services being hosted at
  a single endpoint, for simplicities sake.
- Consolidates the concept of clients across a couple separate terms.

Adding some missed prettifying.

Author: toumorokoshi

aep/general/0003/aep.md

@@ -0,0 +1,106 @@
+# Glossary
+
+This AEP defines common terminology.
+
+## Guidance
+
+The following terminology **must** be used consistently throughout AEPs.
+
+### API
+
+Application Programming Interface. This can be a local interface (such as an
+SDK) or a Network API (defined below).
+
+### API Backend
+
+A set of servers and related infrastructure that implements the business logic
+for an API Service.
+
+### API Client
+
+An API Client is a program or library that perform a specific tasks by calling
+an API or generic tools, such as CLIs, that expose the API in a user-accessible
+fashion or operate on resource data at rest.
+
+Examples of clients include the following:
+
+- Command line interfaces
+- Libraries, such as an SDK for a particular programming language
+- Scripts that operates on a JSON representation of a resource after reading it
+  from an API
+- Tools, such as a [Declarative client][]
+- Visual UIs, such as a web application
+
+### API Definition
+
+A well-structured representation of an API Service.
+
+### API Endpoint
+
+Refers to a network address that an API Service uses to handle incoming API
+Requests. One API Service may have multiple API Service Endpoints, such as
+`https://pubsub.example.com` and `https://content-pubsub.example.com`.
+
+### API Gateway
+
+One or more services that together provide common functionality across API
+Services, such as load balancing and authentication.
+
+### API Method
+
+An individual operation within an API. It is typically represented in Protocol
+Buffers by an `rpc` definition, or in HTTP via a `method` and a `path`.
+
+### API Request
+
+A single invocation of an API Method. It is often used as the unit for billing,
+logging, monitoring, and rate limiting.
+
+### API Resource
+
+An object upon which one or more API methods operate.
+
+### API Resource Type
+
+An API resource type represents a category of that consumes and API,
+
+### Consumer
+
+Either a programmatic client or a user that consumes an API. This term should
+be used when a statement refers broadly to both programs and users.
+
+### Declarative Clients
+
+Declarative Clients, also known as Infrastructure as Code (IaC), describes a
+category of clients that consumes a markup language or code that represents
+resources exposed by an API, and executes the appropriate imperative actions to
+drive the resource to that desired state. To determine what changes to make and
+if a set of updates was successful a declarative client compares server side
+resource attributes with client defined values. The comparison feature ensures
+accuracy of a creation or an update but it requires services to treat the
+client set fields as read-only and diligently preserve those values.
+
+Examples of complexities that declarative clients abstract away include:
+
+- Determing the appropriate imperative action (create / update / delete) to
+  achieve desired state.
+- Ordering of these imperative actions.
+
+[Terraform][] is an example of such a client.
+
+### User
+
+A human being which is using an API directly, such as with cURL. This term is
+defined to differentiate usage in the AIPs between a human _user_ and a
+programmatic _client_.
+
+### Network API
+
+An API that operates across a network of computers. Network APIs communicate
+using network protocols including HTTP, and are frequently produced by
+organizations separate from those that consume them.
+
+[Declarative clients]: #declarative-clients
+[Terraform]: https://www.terraform.io/
+
+## Changelog

aep/general/0003/aep.yaml

@@ -0,0 +1,7 @@
+---
+id: 3
+state: approved
+slug: glossary
+created: 2023-11-15
+placement:
+  category: general

aep/general/0126/aep.yaml

@@ -6,4 +6,4 @@ created: 2019-07-24
 placement:
   category: resources
   order: 60
-redirect_from: "/enums"
+redirect_from: '/enums'

aep/general/0151/aep.yaml

@@ -6,4 +6,4 @@ created: 2019-07-25
 placement:
   category: standard-methods
   order: 70
-redirect_from: "/lro"
+redirect_from: '/lro'

aep/general/0211/aep.yaml

@@ -6,4 +6,4 @@ created: 2021-02-24
 placement:
   category: design-patterns
   order: 115
-redirect_from: "/authz"
+redirect_from: '/authz'

aep/general/scope.yaml

@@ -4,13 +4,15 @@ order: 0
 categories:
   - code: meta
     title: Meta
+  - code: general
+    title: General
   - code: resources
     title: Resources
   - code: standard-methods
     title: Standard Methods
   - code: fields
     title: Fields
   - code: operations
-    title: Fields
+    title: Operations
   - code: design-patterns
     title: Design Patterns