The National Park System includes 421 individual park units with at least 19 different naming designations such as national park, national historical park, national seashore, and national recreation area, to list a few.  The various names have evolved over time and generally are meant to be self-explanatory such as national battlefield or national lakeshore.  Regardless of nomenclature, these units are all commonly referred to as “parks”.
The 62 units formally designated as “National Parks” contain a variety of “outstanding natural features and ecological resources” and also typically encompass "large land or water areas to help provide adequate protection of the resources."
The title “National Recreation Area” was originally given to reservoir parks managed by the Bureau of Reclamation.  However, the origins of recreation focused parks go back much further to a national program during the 1930s managed by the NPS to establish “recreational demonstration areas” which developed new or expanded recreation opportunities in proximity to major population centers and to support under-represented communities with a deficit of outdoor recreation. For example, within the Chesapeake Watershed during the 1930s Catoctin Mountain Park and Prince William Forest Park were established and are still managed by the NPS today. More modern and well-known examples of national recreation areas in urban centers include Golden Gate National Recreation Area, Gateways National Recreation Area in New York and New Jersey, and Boston Harbor Islands National Recreation Area. These NPS partnership-oriented examples provide urban access to significant historic resources and important natural areas to offer outdoor recreation opportunities for large numbers of people. National recreation areas often explicitly permit boating, fishing, and hunting. There are currently 18 national recreation areas in the National Park System several of which are among the most visited park units across the nation.