To remove the gray-black vein from the back of a shrimp. This can be done with the tip of a sharp knife or a special tool called a deveiner. On small and medium shrimp, this technique need be done only for cosmetic purposes. However, because the intestinal vein of large shrimp contains grit, it should always be removed.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.