An AWS Region is a geographical area consisting of multiple, isolated data centers known as Availability Zones. These Availability Zones are connected with low latency, high throughput, and highly redundant networking. The description in option B, 'A set of data centers spanning multiple countries,' is incorrect because AWS Regions are within a single country and do not span multiple countries. The correct answer is A, which states that an AWS Region is a specific location within a geographic area that provides high availability through multiple Availability Zones.