Final answer:
An unfunded mandate refers to the situation where state and local governments must comply with federal regulations without receiving sufficient federal funding to cover the associated costs.
Step-by-step explanation:
When state and local governments must conform to costly regulations or conditions to receive grants but do not receive reimbursements for their expenditures from the federal government, this situation is called an unfunded mandate. An unfunded mandate is a federal law or regulation that imposes obligations on state and local governments without fully compensating for the administrative costs incurred.
On the other hand, categorical grants and block grants are types of federal aid that do provide funding, with categorical grants being for specific purposes and block grants offering more flexibility on usage. Revenue sharing was a practice where the federal government distributed funds to state and local entities with few restrictions, but this was abolished in 1986.