Canon is something that has occurred in a series, contrary to non-canon, where something is simply made up. I think Femslash, means a lesbian relationship, または simply just lesbian sex. I might be wrong.
Canon means something that is showed to be a fact in a fandom. Like Spider-man dating and/or marrying Mary Jane Watson is canon.
Spider-man dating Black Widow would be fanon. As in a ship formed によって the ファン and it would stay fanon unless the creators actually allow Spidey to 日付 Black Widow.
スラッシュ is virtually a pairing (couple that ファン create) but スラッシュ is normally used in conjunction with "slash pairing" Normally if I remember correctly it could be male x male または hetero pairing. And femslash is for female x female pairing.
Before あなた ask または anyone else no I don't consider myself a shipper. I am フレンズ with a bunch of them. And while I do like some pairings. I am not crazy for them によって any means.