Final answer:
Route summarization is the process that reduces the size of the routing table by advertising a single route as a destination for a group of contiguous subnets.
Step-by-step explanation:
The process that reduces the size of the routing table by advertising a single route as a destination for a group of contiguous subnets is Route summarization. Route summarization, also known as supernetting, is a technique used in IP routing to aggregate multiple network routes into a single route advertisement. This helps to reduce the size of the routing table and improve network efficiency.