The Chiltern Hundreds are small area in England that used to have their own local administration (a "hundred" is a collection of villages). The Stewardship of the Chiltern Hundreds has been a do-nothing job for centuries, but is carefully preserved for this reason:
Nobody can resign from Parliament as such. However, no M.P. can hold an "office of profit or trust", an obvious anti-corruption measure. Therefore, to resign from Parliament, one applies for the Stewardship of the Chiltern Hundreds, an office of profit (it pays a salary), is forthwith no longer an M.P., and then resigns the Stewardship.