From BR Bullpen

The grandstand is the portion of a ballpark where permanent seating has been built to accomodate spectators. In modern major league ballparks, all of the field is surrounded by a permanent grandstand, but that is not the case in most minor league parks, or in older parks, where permanent seats are only present in certain areas.

The grandstand can take a variety of shapes. Most common is a "V" or "U" shape with the tip behind home plate, but grandstands also exist in an "L" or "J" shape, with most of the seating behind one of the two base lines, or as a simple rectangle either behind the plate or behind the line. The grandstand is usually tiered, with either individual seats or benches providing a place for spectators to watch the game. It can be double or even triple-decked; the grandstand is sometimes covered by a roof providing shade or protection from the elements. The flat areas where seats are laid out in front of the grandstand are the boxes. Other areas where spectators can watch the game include the bleachers, which are like mini grandstands behind the outfield fence, or general admission areas, where spectators sit or stand along the foul lines or behind the outfield.

The first grandstands, in the second half of the 19th century, were built of wood and were similar to what one would find today at a high school stadium; they would often burn down. The first permanent concrete and steel grandstands were built at the beginning of the 20th century, with Cincinnati's Palace of the Fans and Philadelphia's Shibe Park among the earliest examples.