Chiltern Hundreds
/ˌtʃɪlt(ə)n ˈhʌndrədz
/(In the UK) a Crown manor, whose administration is a nominal office for which an MP applies as a way of resigning from the House of Commons. This is because stewardship of the district is legally an office of profit under the Crown, the holding of which disqualifies a person from being an MP.
Origin
From Chiltern Hills and Hundreds (see the hundred (noun)).