I followed a link to a download on a website called Sourceforge and was asked to pick a mirror. The file downloaded fine, but what’s a mirror?
A mirror is a different website that has a copy of the file for you to download. It helps the main site by offloading the strain that a site may experience due to a number of people wanting to download the same tile at the same. So, while your girlfriend may think that a mirror is somewhere she can apply face moisturizer with, in the computer worlds it’s something completely different.
The great thing about Sourceforge is that most of its mirrors are reputable, so just pick the closest one, it doesn’t matter which one you’ll select.