Jacobites were people whom the English army opposed in Scotland during the early to mid 18th century. They stood for getting rid of the Hanoverian monarchy in favour of Bonnie Prince Charlie and his family.
When imprisoned in an English jail with Jamie McCrimmon and Ben Jackson on 16 April 1746, the Second Doctor was called a "Jacobite pig" by a British sentry. The Doctor had provoked the reaction by shouting, "Down with King George!" When asked by Jamie whether that meant he was pro-Prince Charles, the Doctor replied, "No, not really. I just like hearing the echo, that's all." (TV: The Highlanders)