Long nocks refer to the the longer center nock of the arrows on the reverse of a Morgan dollar.
Long nocks are only found in the 1878 series... ALL 8tf coins have long nocks. The 7/8tf coins are long nocks, as well as the B1 reverses (1878-P VAMs 70-86). There are some 1878-cc long nocks, and ALL of the 1878-s long nocks are TOP-100 coins. Note that not all long nocks are TOP-100 coins, with the exception of 78-s.