What does "non-linear" editing mean?

Prior to digital editing, video editing was achieved through "linear editing." In "linear editing" the finished product is built as edit decisions are made. Therefore, if you were working on a 10-minute video and needed to fix something in the first 2 minutes, your new edit could throw off everything that came after it, requiring you to rebuild all the video after the new edit. With "digital non-linear editing" all edit decisions are made before the finished product is built. Editing this way allows the editor to test edits and preview the finished product before exporting the video to more permanent media.