This is the region (eg. Europe) that a stock trades in. For example, if a stock trades on the London Stock Exchange or the Oslo Stock Exchange, then the stock's region would be Europe.
Users can use this field to filter for companies that trade in a specific region. This field may be useful because some brokers only facilitate trading within particular countries or regions. As such, users can use this field to find companies that their brokers can trade. This field may also be useful for users who want to diversify their portfolio holdings beyond a given region. For example, if a user only holds European stocks, they may want to search for companies that trade in other regions, in Asia for instance.