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+# Glossary
+
+This document describes some commonly-used terms in discussions of federation.
+
+## `ActivityPub`
+
+A decentralized social networking protocol based on the ActivityStreams data format. See [here](https://www.w3.org/TR/activitypub/).
+
+GoToSocial uses the ActivityPub protocol to communicate between GtS servers, and with other federated servers like Mastodon, Pixelfed, etc.
+
+## `ActivityStreams`
+
+A model/data format for representing potential and completed activities using JSON. See [here](https://www.w3.org/TR/activitystreams-core/).
+
+GoToSocial uses the ActivityStreams data model to 'speak' ActivityPub with other servers.
+
+## `Actor`
+
+An actor is an ActivityStreams object that is capable of performing some Activity like following, liking, creating a post, reblogging, etc. See [here](https://www.w3.org/TR/activitypub/#actors).
+
+In GoToSocial, each account/user is an actor.
+
+## `Dereference`
+
+To 'dereference' a post or a profile means to make an HTTP call to the server that hosts that post or profile, in order to obtain its ActivityStreams representation.
+
+GoToSocial 'dereferences' posts and profiles on remote servers, in order to convert them to models that GoToSocial can understand and work with.
+
+Here's a more detailed explanation with some examples:
+
+Let's say that someone on an ActivityPub server searches for the username `@tobi@goblin.technology`.
+
+Their server would then do a webfinger lookup at `goblin.technology` for the username `tobi`, at the following URL:
+
+```text
+https://goblin.technology/.well-known/webfinger?resource=acct:tobi@goblin.technology
+```
+
+The `goblin.technology` server would give back some JSON in response; something like this:
+
+```json
+{
+  "subject": "acct:tobi@goblin.technology",
+  "aliases": [
+    "https://goblin.technology/users/tobi",
+    "https://goblin.technology/@tobi"
+  ],
+  "links": [
+    {
+      "rel": "http://webfinger.net/rel/profile-page",
+      "type": "text/html",
+      "href": "https://goblin.technology/@tobi"
+    },
+    {
+      "rel": "self",
+      "type": "application/activity+json",
+      "href": "https://goblin.technology/users/tobi"
+    }
+  ]
+}
+```
+
+Under the links section the requesting server would look for a link of type `application/activity+json`, which denotes the ActivityStreams representation of the user. In this case, the URL is:
+
+```text
+https://goblin.technology/users/tobi
+```
+
+The above URL is a *reference* to the activitypub representation of the user/Actor `tobi` on the `goblin.technology` instance. It's called a reference because it doesn't contain all of the information about that user, it's only a reference point for where that information can be found.
+
+Now, the requesting server will make a request to that URL in order to obtain a fuller representation of `@tobi@goblin.technology`, which complies to the ActivityPub spec. In other words, the server now follows a *reference* to get to the thing it references. This makes it *not a reference anymore*, hence the term *dereferencing*.
+
+For an analogy, consider what happens when you look something up in the index of a book: first you get the page number that the material you're interested in is on, which is a reference. Then you turn to the referenced page to see the content, which is dereferencing.