According to Fred Turner in From Counterculture to Cyberculture legitimacy exchange is…

…a term that refers to the process by which experts in one area draw on the authority of experts in another area to justify their activities.

and it follows interestingly with

As Bowker explains, “An isolated scientific worker making an outlandish claim could gain rhetorical legitimacy by pointing to support from another field–which in turn referenced the first worker’s field to support its claim. The language of cybernetics provided a site where this exchange could occur.”

The other term I took from the book is “network forum” in which individuals from different fields can meet and exchange legitimacy. Turner’s book gives the Whole Earth Catalog as a print example.