In decentralised social networks, many terms can be confusing for people. Some words are technical and difficult to understand. People new to this technology often get lost in the special vocabulary. This glossary provides simple explanations to help you understand these concepts better
ActivityPub – the open internet protocol that powers most of the fediverse.
Fediverse – name given to the network that is mostly powered by ActivityPub. Mainly used to describe the network that consists of servers running software like Mastodon, PeerTube, Lemmy and much more.
AT Protocol – The open internet protocol that powers Bluesky and other applications build with it. Also known as atproto or ATProto.
ATmosphere – The name of the network that uses AT Protocol.
Bluesky – the microblogging social networking platform.
Bluesky PBC – Bluesky Public Benefit Company. The company that develops and maintains the Bluesky platform and the AT Protocol. The PBC is added to distinguish between Bluesky the app and Bluesky the company.
Microblogging – Sending out short posts on a platform like Twitter, X, Threads, Mastodon, Bluesky and more.
Long-form articles – Articles/blogs/newsletters that are not microblogs. This specific term is used to put it in contrast with microblogging, and is mainly used in the fediverse in technical conversations.
Misskey – A microblogging platform that uses ActivityPub. Mainly popular in Japan.
*key – Term to refer to the entire group of platforms that are all forks of Misskey, such as IceShrimp, Sharkey, Firefish and more.
Mastodon – The most popular microblogging platform that uses ActivityPub.
Toot – A term originally used by Mastodon to describe a post, similar to how a post on Twitter used to be called a Tweet. Still in use by parts of the community, but officially depreciated by Mastodon.
Server – The term server or instance as it is used on the fediverse refers to an independent node in the network, that connects with other servers on the network, usually using the ActivityPub protocol.
Instance – see server.
Local-only posting – Posts made on a server that are not intended to reach other servers in the network, and are only visible to other accounts on that server. Not all fediverse software does support local-only posting, notably Mastodon does not.
Fork – A software fork is when people use existing code of open source software and make their own version, maintained by different people. The fork often works similar to the original software with modifications to suit the needs of the people who build and maintain the fork.
Lexicon – A schema system used by AT Protocol that defines data types. It allows applications that use AT Protocol to understand what things like posts, profiles, and follows mean in the protocol. It can be compared to a file type, similar to how there are file types for .jpg and .gif for images, there are multiple lexicons on AT Protocol to describe data on the network.
PDS (Personal Data Server) – A PDS stores all the data of an account on AT Protocol. All PDS data is public.
AppView – A service on AT Protocol. It can be anything from a simple app like Statusphere or a complex social media platform like Bluesky.
Relay – A component of the AT Protocol network that listens to all activity on the entire network, and broadcasts as a continuous stream of events (posts, likes, follows, etc).
Relay (if used in context of Nostr) –
Firehose – An informal name for the output of a relay.
Labeler – A service that can apply labels to content such as “adult content” or “misleading,” helping users filter what they see. Labels don’t actually remove content but provide information so users can make filtering decisions themselves.
DID (Decentralised IDentifier) – A globally unique identifier that doesn’t require a central registration authority. There can be various versions (‘methods’) of DIDs, indicated by a DID:[type].
DID:PLC – PLC stands for Public Ledger of Credentials, and DID:PLC is the ‘DID method’ most commonly used by Bluesky PBC and AT Protocol.
Fediblock – a popular hashtag used on the fediverse to alert others within the community of potential bad actors that are worth blocking. Mainly used for server-to-server blocks, although sometimes also used to warn against individual accounts.
Nostr – A social media protocol, that focuses on censor-ship resistance, using cryptographic keys instead of servers to verify user identities. Nostr is separate
Open Social Web – A broad term to describe the collective of interoperable networks, which includes platforms build on ActivityPub, AT Protocol, Nostr, and more.
Handle – A username.
OAuth – A protocol that allows people to log in to another service without having to share their password.
Ozone – Open source software used for moderation on AT Protocol, build and maintained by the Bluesky company.
IFTAS – A non-profit organisation for trust and safety in the fediverse.
Threadiverse – A term used to describe the collective of link aggregator platforms on the fediverse, such as Lemmy and Piefed
Link aggregator – A technical term to describe platforms that function similar to Reddit. Examples on ActivityPub are Lemmy and PieFed, and Frontpage on AT Protocol.
Bridging – Making different protocols interoperable.
Bridgy Fed – A well-known software tool that allows for bridging between most open protocols.
SWICG – Social Web Incubator Community Group. Part of the W3C and consists of volunteers that are working on maintaining the ActivityPub specification.
W3C – World Wide Web Consortium. Is responsible for administrating a variety of open web standards, including ActivityPub.
ActivityStreams – A standardised format for representing social activities, actions, and updates. It is a part of the ActivityPub protocol.
Webfinger – A protocol to discover information about a user. Used by many fediverse services, although it is not officially part of the ActivityPub protocol.
Threads – A microblogging platform made by Meta.