Double-decker bus
The first commercial horse-drawn double-decker omnibuses were introduced in England in 1847 by Adams & Co. of Fairfield, Bow, then improved upon by John Greenwood, who introduced a new double-decker in 1852.
Rigid bus
Rigid buses may be of either single-deck or double-deck design, and may have either two axles or multi-axles. However, the expression "rigid bus" is seldom used to describe a double-decker bus, because very few double-decker buses have anything other than a rigid chassis.