This is a dirty air conditioning filter. If a filter is this dirty oh, your air conditioner will struggle to overcome the obstruction. This causes the system to work harder than necessary, which can shorten the system's life. Just like teeth, air conditioning systems benefit from regular cleanings so that they can function as intended. Aside from changing your filters, it is a good idea to have the entire system cleaned on a semi-annual basis. The cooling coil, blower wheel, condenser fins, drain...