Amounts due under a lease in addition to the originally agreed upon base rent. Leases usually characterize all sums due to a landlord,including late fees,collection costs,and property damage, as additional rent.This gives the landlord some legal advantages as far as declaring a default,obtaining an eviction,and collecting sums due.Examples could include the tenant's share of property maintenance and insurance expenses and a retail tenant's obligation to pay a percentage of gross income in addition to base rent.