A pre-roll is another word for joint. In this case, one that is already “pre-rolled” when purchased.
They tend to be rolled in a cone style with a folded paper mouthpiece.
Empty pre-rolls are sold: from mini-dogwalker (1/3 gram), dog walkers (1/2 gram) or a full gram.
They are convenient. Easy to use. And come in many styles and colors.
This is a good way to try out different strains without making a huge investment.