An Activity is a subtype of Object that describes some form of action that may happen, is currently happening, or has already happened. The Activity type itself serves as an abstract base type for all types of activities. It is important to note that the Activity type itself does not carry any specific semantics about the kind of action being taken.

ActivityPub actors are generally one of the ActivityStreams Actor Types, but they don't have to be. For example, a Profile object might be used as an actor, or a type from an ActivityStreams extension. Actors are retrieved like any other Object in ActivityPub. Like other ActivityStreams objects, actors have an id, which is a URI. When entered directly into a user interface (for example on a login form), it is desirable to support simplified naming.

Describes a software application

Represents any kind of multi-paragraph written work

Represents an audio document of any kind

A Collection is a subtype of Object that represents ordered or unordered sets of Object or Link instances.

Used to represent distinct subsets of items from a Collection.

Represents a document of any kind

Represents any kind of event

Represents a formal or informal collective of Actors

An image document of any kind

Instances of intransitiveActivity are a subtype of Activity representing intransitive actions. The object property is therefore inappropriate for these activities.

A Link is an indirect, qualified reference to a resource identified by a URL. The fundamental model for links is established by [RFC5988]. Many of the properties defined by the Activity Vocabulary allow values that are either instances of Object or Link. When a Link is used, it establishes a qualified relation connecting the subject (the containing object) to the resource identified by the href. Properties of the Link are properties of the reference as opposed to properties of the resource.

A specialized Link that represents an @mention.

Represents a short written work typically less than a single paragraph in length.

Describes an object of any kind. The Object type serves as the base type for most of the other kinds of objects defined in the Activity Vocabulary, including other Core types such as Activity, intransitiveActivity, Collection and OrderedCollection.

A subtype of Collection in which members of the logical collection are assumed to always be strictly ordered.

Used to represent ordered subsets of items from an OrderedCollection.

Represents an organization

Represents a Web Page

Represents an individual person

Represents a logical or physical location. See 5.3 Representing Places for additional information.

A Profile is a content object that describes another Object, typically used to describe Actor Type objects. The describes property is used to reference the object being described by the profile.

Represents a question being asked. Question objects are an extension of IntransitiveActivity. That is, the Question object is an Activity, but the direct object is the question itself, and therefore it would not contain an object property.

Describes a relationship between two individuals. The subject and object properties are used to identify the connected individuals. See 5.2 Representing Relationships Between Entities for additional information.

Represents a service of any kind

A Tombstone represents a content object that has been deleted. It can be used in Collections to signify that there used to be an object at this position, but it has been deleted.

Represents a video document of any kind