The Solar Return is a chart calculated for the exact time when the Sun returns to the precise position it occupied when you were born, that is, to the exact position indicated in your birth chart. This happens once a year around your birthday, usually at a different time from when you were born, and in some cases a day after or a day before your birthday.
The Solar Return marks the main events of the year from birthday to birthday. It's a bit like starting a new year on your birthday. The Solar return is also calculated according to the location of your Solar Return, that is to say the place where you were or the place where you will be at the time of your birthday; naturally, some places are more favorable than others.
With multiple returns calculated for different locations, you could analyze the changes arising from the different locations and choose the most appropriate place to spend your birthday.