A Sedan was a type of vehicle, designed to be carried by people.
Sedans were in use in one historical period of Sarpeidon, as could be seen with the help of the Atavachron. (TOS: "All Our Yesterdays")
T'Pau arived at Spock's Koon-ut-kal-if-fee in a sedan. (TOS: "Amok Time")
The script refered to this vehicle as a "sedan litter"
A sedan chair was also mentioned in the script of "Cost of Living", but the scene in which it was was cut from the final episode.