排挡 refers to a vehicle's transmission/gear position. Often shortened to just
挡 (dǎng) —
一挡,
二挡,
三挡 (1st, 2nd, 3rd gear).
手动排挡 = manual transmission,
自动排挡 = automatic. Distinguish from
大排档 (dàpáidàng — open-air food stall) which uses
档 (also pronounced dàng/dǎng) but is a totally separate word.