A midibus is a classification of single-decker minibuses which are generally larger than a traditional minibus but smaller than a full-size single decker and can be anywhere between 8 metres and 11 metres long. While used in many parts of the world, the midibus is perhaps most common in the United Kingdom, where operators have found them more economical, and to have a sufficient number of seats compared to full size single-decker buses.

The Albion Nimbus was an underfloor-engined, ultra-lightweight midibus or coach chassis, with a four-cylinder horizontal diesel engine and a gross vehicle weight of six tons. It was largely operated on light rural bus duties and private hires. Operators who used it on heavy-duty bus routes found it insufficiently robust. It was the first Albion bus chassis to have a name that did not begin with the letter V. The design was revised twice and was produced from 1955 to 1965.