What the General Prologue offers is a brief, often very visual description of each pilgrim, focusing on details of their background, as well as key details of their clothing, their food likes and dislikes, and their physical features. These descriptions fall within a common medieval tradition of portraits in words (which can be considered under the technical term ekphrasis), Chaucer's influence in this case most likely coming from The Romaunt de la Rose.
Immediately, our narrator insists that his pilgrims are to be described by 'degree'. By the fact that the Knight, the highest-ranking of the pilgrims, is selected as the first teller, we see the obvious social considerations of the tale. Still, all human life is here: characters of both sexes, and from walks of life from lordly knight, or godly parson down to oft-divorced wife or grimy cook.
Each pilgrim portrait within the prologue might be considered as an archetypal description. Many of the 'types' of characters featured would have been familiar stock characters to a medieval audience: the hypocritical friar, the rotund, food-loving monk, the rapacious miller are all familiar types from medieval estates satire (see Jill Mann's excellent book for more information). Larry D. Benson has pointed out the way in which the characters are paragons of their respective crafts or types - noting the number of times the words 'wel koude' and 'verray parfit' occur in describing characters.
Yet what is key about the information provided in the General Prologue about these characters, many of whom do appear to be archetypes, is that it is among the few pieces of objective information - that is, information spoken by our narrator that we are given throughout the Tales. The tales themselves (except for large passages of the prologues and epilogues) are largely told in the words of the...