A private bill is a piece of legislation that gives powers or benefits to a particular group of persons, such as a local council or private corporation.
These changes to the law do not affect the general public as a whole.
A private bill might be introduced, for example, to give Railtrack the power to construct a new railway line in a particular area of the country.
Under special procedures covering private bills individuals likely to be affected by them, such as people whose houses are in the way of a planned railway line, are able to petition Parliament.
A panel of MPs will hear their objections and judge whether the bill's supporters must either withdraw the bill or alter it so that it does not harm the petitioners.
Occasionally private bills affecting just one or two people are brought before Parliament. These are known as personal bills.