intr.v. trick-or-treat·ed, trick-or-treat·ing, trick-or-treats
To engage in the practice of asking for treats on Halloween and threatening to play tricks on those who refuse.
The likely origin is the medieval custom of dressing in disguise and going door to door begging for food or coin. In some areas the begging was accompanied by threats to cause mischief.
The first recorded example in North America was in 1911, where a newspaper in Kingston, Ontario reported it in the Scottish form of "guising".