A moped was a form of transport used on Earth in the 20th century. It was ridden in a similar manner to a bicycle or motorbike.
The Tenth Doctor had a blue Vespa moped which he and Rose Tyler rode when visiting London during the Coronation of Queen Elizabeth II. (TV: The Idiot's Lantern)
The Eleventh Doctor also referred to a space vehicle of similar design as a moped. (TV: The Rings of Akhaten)