"Chokepoint" is a strategy term that refers to any enclosed space, corridor, or area where large numbers of players are forced to pass through, with no alternate routes. Typically, a chokepoint will be preceded by open spaces. For example, a narrow corridor or doorway may be known as a chokepoint if it connects to a wide open area. Chokepoints are important elements to consider strategically, as it enables the player to ambush an area more effectively due to the nature of a chokepoint's closed space, and is prone to contain explosive spam and area denial tactics.
In Team Fortress 2, many maps vary between tight and wide open spaces in order to provide proper balance to all classes and teams, depending on the map that is played on. Common chokepoint placement on maps in the game include turns and bends of the track path in Payload maps, and between capture points on Control Point maps. They are also seen as narrow corridors that are present in many other maps, such as attack and defend maps, such as Dustbowl.
A Spy could also utilise these areas by waiting for an enemy to pass through, and follow up with a lethal Backstab for precision elimination. Be careful not to go through narrow chokepoints that won't fit two people side-by-side.
A Sniper does not really benefit in chokepoints other than lining up enemies into a tighter area. However, the Machina was designed for this type of situation, potentially killing many enemies with a well placed shot. The Jarate is also useful for this type of situation, making your enemies more vulnerable to the already ridiculous amounts of damage.
A Soldier can spam rockets without worrying too much about accuracy due to splash damage. This also makes juggling easier if you are going for accuracy. The cramped area also benefits a lot from the battle banners, namely the Buff Banner, the Battalion's Backup and the Concheror. The Cow Mangler 5000 and the Beggar's Bazooka are also useful for this situation: The former has a charged shot that mini-crits and sets enemies on fire and the latter has ridiculous amounts of splash damage with a three rocket burst.
A Medic doesn't have too much of an advantage, as most classes will be able to outmatch the Syringe Gun in terms of damage per second. That said, a Medic can greatly enhance an ally camping a chokepoint, especially if he is using the Kritzkrieg.
A Demoman has many advantages here: He may use his Grenade Launcher to a greater extent and the spam might help conceal Stickybombs. The cramped area also allows for maximizing splash damage, something a Demoman is notorious for.
An Engineer can focus his Sentry Gun for superb area control, but due to chokepoints being only one corridor, there aren't many uses for it. Also, a Dispenser can be built to provide health and ammo to spamming allies and a Teleporter for respawned teammates to get to the chokepoint fairly quick.