A cot was a type of portable bed.
In 1930, Edith Keeler offered a recovering Leonard McCoy use of a cot in the back room of the 21st Street Mission. (TOS: "The City on the Edge of Forever")
In 2373, Quark described his "cabin" aboard a runabout bound for Risa as "a cot and a waste disposal unit." (DS9: "Let He Who Is Without Sin...")