Pork shoulder is also known as picnic ham. Not really a true ham (which comes from the pig's back leg), the picnic ham is taken from the upper part of the foreleg and includes a portion of the shoulder. This cut is also more accurately referred to as the picnic shoulder or pork shoulder. The picnic ham is smoked, which gives it a very ham-like flavor. It often has the bone removed. Though it's slightly tougher (requiring longer cooking) and has more waste because of the bone structure, picnic ham is a good, inexpensive substitute for regular ham.
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.