It is used to differentiate the country the dvd/hddvd etc... was released in. A good clue is the rating on the title as these are specific to the countries of release. Although to be unhelpful you will find some releases have multiple ratings, european music titles do this a lot and 'UK' releases usually have both the UK and Irish ratings on them, so could use either UK or Ireland.

Yes and no to your second question about locality and results from the online, if you add by EAN it effectivley ignores locality, if you add by title it will default to your locality for the results displayed, you can change which regions are displayed from a drop down on the add by title page.

Edit - to explain why locality is useful, region codes cover a large area, locality allows us to enter titles that have the same UPC/EAN but are released in different countries in the same region code, e.g. if a title is released in the UK and Germany with the same UPC they would have different covers/languages but without locality only one could be entered into the database.

Hi, welcome to the forum!

For most, locality equals country. Only in one case there are multiple localities in a country: Canada (meaning English) and Canada (Quebec) (meaning French). See back cover for the Canadian age certificate and the overview in french-only to classify it as Canada (Quebec).

Also locality covers recent (as in: since DVD profiler came into existence...) world history changes, like Sovjet Union for older movie titles and Russia (or other names of the republics that came into being after the USSR break-up) for newer. Likewise the breakup of Yugoslavia. Or Hong Kong (semi-independent in the UK) that became part of China later, meaning a lot of martial arts movies can be either one, depending on the age of the title.

As for titles that remain unallocatable to a locality (meaning age certificate logo or language are not the dead giveaways), it is problably safe to use the U.K. or the U.S. as locality. Just read the back cover carefully: for a person from the U.K. an american text usually contains a horrible amount or spelling errors. For details, see for instance this... 
An U.S.A. originating disk usually starts with a FBI warning about piracy. However, any back cover clues should take precedence since HD-DVD's are region free and the same pressing could have been sold in multiple countries.

Quoting eommen:

Quote:
... For most, locality equals country.

But which country is the key. New users should understand that the locality may be equal to, but is not always the same as Country of Origin, Country of Production or Country of Purchase.

In the current release of DVD Profiler, Ken has made it possible for people who understand XML, such as plugin and tools programmers, to get precise information about Locality. This information is in the Localities.XOD file in Program Files\DVD Profiler\Media folder. Take a look - it is interesting and informative.

(Edit: I should have followed the link in deejay's post. That Wiki article is great. I would assume that the Localities.XOD correlates to the Wiki info. - I didn't check it carefully yet.)

Here is a small excerpt:

<Locality Description="Argentina" ID="32" DVDRegion="4" BDRegion="A">
<Ratings Description="Film" ID="0">
<Rating LegacyValue="1" Name="ATP" Description="ATP" Age="1"/>
<Rating LegacyValue="3" Name="PM13" Description="PM13" Age="13"/>
<Rating LegacyValue="4" Name="PM16" Description="PM16" Age="16"/>
<Rating LegacyValue="5" Name="PM18" Description="PM18" Age="18"/>
</Ratings>
</Locality>
<Locality Description="Australia" ID="2" DVDRegion="4" BDRegion="B">
<Ratings Description="Film" ID="0">
<Rating LegacyValue="1" Name="G" Description="General" Age="1"/>
<Rating LegacyValue="2" Name="PG" Description="Parental guidance recommended" Age="10"/>
<Rating LegacyValue="3" Name="M" Description="Recommended for mature audiences" Age="13"/>
<Rating LegacyValue="4" Name="MA 15+" Description="Not suitable for people under 15. Under 15s must be accompanied by a parent or adult guardian" Age="15"/>
<Rating LegacyValue="5" Name="R 18+" Description="Restricted to 18 and over" Age="18"/>
<Rating LegacyValue="6" Name="X 18+" Description="Restricted to 18 and over" Age="18" Variant="1" Adult="True"/>
</Ratings>
</Locality>