Canon is a concept concerning the truthfulness of events portrayed as being part of (or related to) a narrative, from the perspective of a particular framework that considers all parts of the narrative nominally seen as canon to be entirely true with relation to each other within the narrative. This is in contrast to non-canon events or depictions, such as speculative derivative works (fanfiction) and the like, which may use elements, settings or characters from a narrative, but are not considered canonical with respect to the narrative proper. Non-canonical works are not considered to be true or "real" from within the main "canonical" body of work.
As a collective noun, a "canon" denotes a collection of distinct works or parts of a work that are together considered to be canonical with respect to each other.
In the Homestuck universe, canon is a tangible aspect of reality that can be interacted with from within the narrative under certain situations. Andrew Hussie, the webcomic's author, also exists as a character within the canon, and can directly intercede in events that occur personally, while it is also acknowledged that he is the one writing the story. More directly, the "treasure" Juju, functioning as a literal "plot hole", is a gateway with which to interact with the canon, as it functions as a physical manifestation of a "narrative breach" that must be filled. John Egbert fills the role of this breach by interacting with the Treasure, granting him the ability to wield Retcon mechanics, powers that let him directly interact with the canonical narrative of Homestuck.
In Act 7, the claiming of the Ultimate Reward through departure to Universe C allows the main cast of the Homestuck canon to leave canon entirely, and exist "out of canon". It is this property that allows for them to escape Lrd English, whose ultimate downfall lies in his existence being bound (or stuck) in a self-perpetuating loop of existence within the Homestuck canon, that begins and ends with his rise to power (and defeat). These two events may be circumstantially simultaneous.
The "out of canon" state that the primary characters find themselves in is a state distinct from non-canonicity, wherein the events that they are living may indeed be "true", but are dependent on the events that occur within the canon. This fact leads to the main crisis of the Homestuck Epilogues; in order for canon to proceed in the manner that will allow these events happening "out of canon" to be "real", then John, who alone can still have a role to play in Homestuck's canon due to his retention of his retcon abilities, must use them to travel back into the Homestuck canon and defeat Lrd English once and for all. Within canon, these may be the events depicted Caliborn's Masterpiece, although this is still speculation. If John fails to do this, then canon will not be able to sustain the "out of canon" events on Earth C, as depicted in the Credits, as real. That reality would be rendered null and void, a process that Rose Lalonde refers to as "dissipation".
Canon, outside canon, and non-canonEdit
List of Homestuck universe works by canonicityEdit