flat rate
noun
1- a charge that is the same in all cases, not varying in proportion with something统一价格, 统一收费; 统一费率：
clients are charged a flat rate of £250 annually
按每年250英镑的统一价格向客户收费
as modifier the flat-rate state pension.统一费率的国家养老金。
1.1
- a rate of taxation that is not progressive, but remains at the same proportion on all amounts均一税率。