geolocation, geoip, geodns, global load balancing are mean the same thing. global load balancing even has its own acronym, GSLB, or global server load balancing.
The industry and it's observers have not yet settled on any standard term. Geodns is certainly more apt when talking about geolocation or geoip applied to dns services. But, it is actually the least prevalent term. Geolocation seems to be the most popular, followed by geoip.
Whatever people call it, in the managed dns service world, it refers to the ability of an authoritative dns server to return distinct records based upon the geographic location of the querying computer. The querying computer is most usually a caching dns server deployed by a consumer internet services provider.
There are very few dns servers that are capable of achieving this. Certainly, no dns software for this task is made publicly available to the mainstream. There are a small number of DNS providers with geographically aware managed dns services. Their underlying software distinguish them from less able competitors. With this in mind, the software is treated as the key intellectual property of such specialists.