Anyone else notice the similarities between Prisoner Zero and Jennifer when she puts her head through the toilet door?

As far as I'm concerned, that scene was not canon. IMO that was a deleted scene that someone forgot to cut...

What do people mean when they say canon?

Canon is nothing. Nothing at all. Pay it no heed. This isn't the canon you're looking for.

On second thoughts, if I can learn to live with the Myrka then I can deal with Jennifer Ganger's dodgy looking stretch...

It's a religious term that basically means something is accepted doctine and not open to debate. Certain events are accepted without question as having happened exactly as described in the Bible but others are regarded as allegorical - more like metaphors and ideals than actual historical events.

In terms of sci-fi and other cult entertainment, it basically means that some things are regarded as factual (within the fantasy world the fiction uses) whilst others aren't. In Doctor Who - like other TV programs - it's generally accepted that anything seen in a broadcast TV episode is "canon" - a fact - but other sources such as books, animated adventures, radio plays and non-series movies are not - unless they are specifically stated as such by the creators/producers of the TV show.

It's a moving target and subject to debate on occasion. For example, if a Doctor Who book had the 9th Doctor getting married to Rose and having a son, that would not be canon because the TV series - the main event - as it were - says it didn't happen. However, if the TV show later included a story that referenced that event - such as meeting this son - that book could then become canon. It's rare but it does happen.

It's sometimes used as Bass_Cadet did - to say that they regard a something as so bad or out of character for the characters or overall tone of the series that they would rather it had never been made and they basically pretend it didn't happen - keeping their own mental image of the Doctor intact.

In comic books, it became so difficult to say what was and wasn't canon -Batman had died or retired a dozen times, Superman would be married to Lois Lane one week and not the next - that they decided to create completely seperate universes and say that anything that didn't fit must have happened in an alternate reality. The odd thing is - the fans still complain when something isn't canon within each universe - they know the stories better than the people who write them.

Personally, I've never had a problem with Doctor Who - but I defy anyone to say that anything involving Scrappy Doo is canon