A Fence Panel, or section, is the part of the fence that sits between two posts (or walls). Panels are composed of one or more horizontal rails that secure a number of vertical pickets, spindles, or balusters.
Fence Panels can be pre-fabricated, as in the case of vinyl and ornamental aluminum, or can be made from boards and rails like the picket fence below. Most panels are either 6 ft. or 8 ft. long depending on the material. Longer than 8 ft. and the panel will sag under its own weight. Any shorter and it would require additional posts and hardware, which would add to the expense.
Most Fences have 2 or more panels anchored and connected by posts.