The various pilgrims cataloged in the General Prologue of The Canterbury Tales give the modern reader a good array of medieval English society. The characters all come from different class backgrounds, united only in their shared destination. English society (and European society at large) was broken down into what was known as the Three Estates: the Clergy, the Nobility, and the Peasantry.
The clergy were those ordained in the church. Bishops, priests, monks, and nuns belong in this category. In Chaucer's story, there are plenty of clergy on the pilgrimage, though they vary in levels of piety. For example, the Prioress acts more like a noblewoman with her affected courtly manners and elegant clothing; the Monk is more interested in hunting than religious contemplation; and the Friar is a womanizer rather than a servant of the poor. Only the Parson is presented as truly dedicated to God. The corruption among the clergy in Chaucer's story is a reflection of the abuses of power within the church during this period, though the presence of the Parson shows that there were still clergy who took their dedication to God and the poor seriously.
The nobility was generally seen as those who fought. This class included the aristocracy and the royal family. In The Canterbury Tales, the nobility is represented by the Knight and the Squire. Both are men of the fighting profession, with the Knight being particularly highlighted as a man of humility and honor.
Finally, the peasantry were the laborers, though some have elected to call this estate the commons, instead, since it included middle-class tradesmen and merchants. For example, the Wife of Bath is neither nobility nor clergy, but she is a merchant who has done well for herself financially. She might not be able to have the same privileges as the Knight or even the clergy members, but she is certainly wealthier than the Clerk or the Miller, who are also part of the peasant/commons class.
Taken altogether, the pilgrims represent medieval English society in all its diversity of class and philosophy. Chaucer gives the reader vital information regarding the background and character of each pilgrim, showing just how complicated both people and society were in the fourteenth century.