Loyalists were Colonists who sided with the British during the revolution. They were also known as "Tories", "Royalists" and "King's Men" and probably also by their enemies as "those bloody arse-kicking ninnyhammers" (among other things).
While being a Loyalist might seem to you like 'the bad guys' that's only because you know the Patriots won. It's very easy to use history to look smart—even if you were subjected to the American education system (and 'system' is a strong word).
In fact, by some estimates as many as one in five Colonists were actively Loyalist—and many more tried not to pick a side altogether.
I expect the version of the story you've heard goes something like this: "The Loyalists were traitors who betrayed their fellow Americans to the British." That's a nice little fiction, since from a Loyalist perspective the opposite was true: the colonies were founded and owned by Britain. The Colonists were therefore British citizens, thus the rebels trying to disobey the king were the real traitors here.
Aha! You see? You're a country of traitors! Try spinning THAT!
You'd also have to be pretty brave to be a Loyalist, particularly if the people in your community were Patriots. Known Loyalists were frequently dragged from their homes, beaten, burned with candles, or tarred and feathered.
That's just in case you suffered from the delusion that the Patriots always took the moral high ground.