Cockpit is a common arcade game form factor.
A cockpit machine is one in which the player is fully enclosed inside the machine, and plays the game sitting down. These are usually driving or flight simulator games, but a few other titles have had cockpit versions released as well.
The first cockpit games were actually electromechanical games, but this form factor didn't really become popular until the late 1970s and early 1980s. During that time period many games were available in cockpit format, with titles such as Sinistar, Turbo, Star Wars, and Pole Position being especially popular with gamers.
Most cockpit games differ from their upright counterparts only in the shape of the machine, but some games (such as Turbo and Pole Position), had other differences as well (the Turbo cockpit had functional gauges, while the Pole Position cockpit had a brake pedal that the upright lacked).
Cockpit machines began to fall out of favor after the early 1980s. They were largely replaced by a new style of ride on machines, that had a seat, but did not enclose the player, almost all modern racing games are like this.
When purchasing a cockpit machine you should always carefully examine the machine to make sure it has never been sawed in half, and then nailed back together (this was actually a real problem with these games). Then check the inside of the game, as cockpit titles tended to have higher vandalism rates, because the enclosure shielded the players from the watchful eyes of arcade employees.
Common cockpit titles (such as Turbo), tend to be cheaper than the upright versions. This is mostly due to the sheer size of the machines. But rarer (or simply more popular), cockpit titles demand premium prices. Expect to pay top dollar for a Sinistar or Star Wars cockpit. A few games had cockpits released in very limited numbers, like Blaster (only three were made), and Missile Command (only 100 were made). The prices for these rare games can easily approach those of a decent used car.