Pilgrim edition?


The marvelous Pilgrim edition of Dickens's letters, in a dozen volumes and profusely annotated, allows us to see the man fully and in all his activities.

What is "Pilgrim edition?" Are the letters about long journey? Or is the phrase some kind of an idiom??? Even after searching many information on Dickens I could only find out there are 12 volumes of "Pilgrim edition" without any further information.
  • If you type Dickens Pilgrim Edition into Google' search is seems to generate quite a bit of information about these texts.
    Yes, I've already searched Google, but I'm not sure what it is.
    Do you think it is a publishing house as foxfirebrand said?