I translated a paragraph below:
JARRET dit BEAUREGARD and Vincent: For different reasons, a few families used these three surnames, sometimes 4. This convention was chosen to indicate the different surnames used by the individual. In the original documents, you will not necessary see the names inscribed this way. In more ways than one the names were written has heard. The names can be as follows: JARRET, BEAUREGARD, VINCENT, JARRET dit BEAUREGARD and Vincent or JARRET dit BEAUREGARD dit VINCENT.
The following links are in french and may help you understand the concept
http://www.francogene.com/gfan/gfan/998/conventi.htmhttp://www.francogene.com/quebec/comment.phphttp://www.francogene.com/qc-ress/dgo.phphttp://histoiredeweedon.info/?page_id=3714