Money Bills are Bills that deal solely with expenditure – two or three such Bills are passed each year. The Lords are not permitted to amend such Bills and they are rarely discussed in the Upper House. They normally go through all their stages in one day in the Upper House. The Speaker designates a Bill a Money Bill before it arrives in the Lords.
The Finance Bill, which enacts the Chancellor's annual budget, is not technically a Money Bill – it is a Bill of aids and supplies. Nevertheless, the Lords treat it as though it were a Money Bill. The 'privilege' of the Commons on financial arrangements has long been accepted. Amendments on such issues are called 'privilege amendments' and are accepted without question by the Upper House.