Definition of "Rap"

Rap

proper noun
1. (slang, attributive) The Rapaport Diamond Report, the diamond industry standard for the pricing of diamonds.
  Quotations
  He makes good sense. However, I must comment on "CSO prices rough diamonds to its sightholders based on the Rap List." It does not. It doesn't use the list.
  1996, Jewelers' Circular/Keystone, volume 167, numbers 4-6, page 38
  Soon after the Diamond Certificate came into being, Mr Martin Rapaport edited and published a regular weekly paper based on these official certificates. […] The Rap price is usually way off sometimes by as much as 30% or more.
  2017, Herman Neuman, Secrets of Diamonds