An MCC is a physical change that impacts the profitability or operational capabilities for your business. A typical example would be if you run a shop on the high street and there are road works occurring that are causing a downturn in your footfall.
In these circumstances, you may be able to apply to the Valuation Office Agency (VOA) for a reduction in your rates, for example if you have seen a 20% decline in your turnover caused by a material change, you could in theory appeal to the VOA to have a 20% reduction in your rates.