During a conversation about a something a character was doing in one TV series, someone said that he was too busy doing something else, which referenced another series, implying that it the two series were in a shared universe... we got into an argument of sorts and he challenged me to come here and see what the community think. Now I have my own understanding of canon... but for the purposes of a blind test, me actually posting my ideas which I believe to be true and have had them confirmed to me by several users and people who actually deal with this kind of stuff on a daily basis would be a little pointless. Basically I am here to get the collective or individual opinions of TF fans on three things: 1) What is "canon" (what do YOU think it is?) 2) How does that apply to the TF Multiverse (is there a canon, is it all canon or is none of it canon?) 3) What is there to back up this opinion (is there anything which either proves this or is it just an unwritten rule?) thanks.