A trailhead is the point at which a trail

Trail

A trail is a path with a rough beaten or dirt/stone surface used for travel. Trails may be for use only by walkers and in some places are the main access route to remote settlements...

 begins, where the trail is often intended for hiking, biking, horseback riding, or off-road vehicles. Modern trailheads often contain rest rooms, maps, sign posts and distribution centers for informational brochures about the trail and its features, and parking areas for vehicles and trailers.

Historically, the cities located at the terminus of major pathways for foot traffic such as the Natchez Trace

Natchez Trace

The Natchez Trace, also known as the "Old Natchez Trace", is a historical path that extends roughly from Natchez, Mississippi to Nashville, Tennessee, linking the Cumberland, Tennessee and Mississippi rivers...

 and the Chisholm Trail

Chisholm Trail

The Chisholm Trail was a trail used in the late 19th century to drive cattle overland from ranches in Texas to Kansas railheads. The portion of the trail marked by Jesse Chisholm went from his southern trading post near the Red River, to his northern trading post near Kansas City, Kansas...

 were also known as trailheads.

For mountain climbing and hiking, the elevation of the trailhead above sea level

Sea level

Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

 is given to give an idea of how high the mountain is above the average terrain.