Definition of rotten borough in English:

rotten borough

noun

British
historical
  • A borough that was able to elect an MP despite having very few voters, the choice of MP typically being in the hands of one person or family.

    • ‘It works well in Scotland and now, with PR for Scottish local elections, it breaks up the old Labour rotten boroughs.’
    • ‘The Reform Bill of 1832 redistributed seats from rotten boroughs to populous towns and counties and increased the electorate from 478,000 to 814,000.’
    • ‘Western democracies have had their own experience of rotten boroughs and tribal strongholds.’
    • ‘The city's convoluted electoral system is riddled with rotten boroughs, giving some corporate voters 4,000 times more punch than the votes of ordinary citizens.’
    • ‘The specific reforms he proposed included annual parliaments, publication of their debates and votes, payment of MPs, equalisation of constituencies and the abolition of rotten boroughs.’

Origin

So named because the borough was found to have ‘decayed’ to the point of no longer having a constituency.