Trick or treat

When I was a child, we used to go trick-or-treating on Halloween night. This meant getting dressed up in costumes and going from house to house, knocking on the doors and saying "trick or treat!"
People would usually put some kind of decoration on the house to show that they were ready for trick-or-treaters, like a jack-o-lantern, one of those pumpkins with a face and a candle inside.
Trick or treat means: choose between giving us a treat (candy) or having us do something mean (a trick). Of course, everyone chose to give a treat! But there were some tricks in the neighborhood too, like teenage boys who would decorate someone's house in toilet paper. in general, though, the kids who went trick-or-treating received a plenty of candy and had a good time seeing neighbors and friends with their decorated houses...