Historically it has mainly been used on a country level to ensure that content is in the same language as the users it is reaching.
However, geo-targeting is now being used widely for mobile advertising to tell users about real-world locations as they are on the move.
For example, a shop could pay to advertise to anyone within a five-mile radius that they are having a sale. With smartphones being so prevalent, this means that people who were travelling through that geo-targeted area could also see those ads (instead of people who simply live nearby).
This change in users internet browsing behaviour (from static locations to on-the-go) has made geo-targeting incredibly useful and important to advertisers.Glossary Index