From: Steve Rogerson steve.rogerson@mcr1.poptel.org.uk
Canon is anything that happened in the 52 TV episodes and two BBC radio
plays (I
know some do not include the radio plays) and nothing more.
A story is within the boundaries of canon if it does not contradict
anything that
is in canon (such a story is not in itself canon).
A story is non-canonical if it contradicts what is in canon.
My own definitions (made up here on the spot, though I've used them rather more loosely in the past) -
Canonical - actually there, in the series (not the radio plays), for all to see. Subcanonical - an interpretation of the canon that does not contradict it. Extracanonical - an addition to the canon that is neither supported by the canon nor directly violates it. Noncanonical - a flat contradiction of the canon.
So, taking a particular incident that has recently come under the spotlight: Canon - Blake kissed Inga Subcanon - Blake loved Inga (an interpretation of the kiss) Extracanon - Blake was the father of Inga's illegitimate child who was taken away from her at birth by the Morality Police, inspiring Blake to join the Freedom Party and vow to overthrow the Federation (invented backstory that canon neither supports nor refutes). Noncanon - 'Inga' was really Tarrant in disguise.
Neil