GeoDNS
GeoDNS (also called geo-aware DNS or DNS-based traffic steering) is the practice of returning different DNS answers depending on where the query came from. A US visitor to example.com might get a US-east IP, while a European visitor gets a Frankfurt IP — both correct, both legitimate.
How it works
The authoritative nameserver inspects the IP address of the recursive resolver making the query (or, with the EDNS Client Subnet extension, the original client's subnet). It then returns the record best suited to that location based on rules you configure: closest data center, healthiest endpoint, country-specific compliance, etc.
Common providers
Cloudflare Load Balancing, AWS Route 53 traffic policies, NS1, Akamai, and most modern CDNs implement some form of GeoDNS. If you've set up "geo-routing" or "latency-based routing" in any of those, that's GeoDNS.
How to verify GeoDNS is working
Run a lookup through WhereIsDNS for an A record. If the resolvers in different regions return different IPs that all belong to your service, GeoDNS is working as intended. If they all return the same IP, either GeoDNS is misconfigured, the resolver isn't sending the client subnet, or only one location is healthy.
Common confusion
GeoDNS results can look like a propagation problem when they're actually correct behavior. If consensus is split across regions but each region's answer matches your expected geography, that's GeoDNS, not a stale cache.