Wondering how Spotlight works, or why it can’t find a file that you were SO SURE you had saved on your hard drive? Turns out that Spotlight is in essence an index of all the metadata from the files on your hard drive. When you type in a search query, the app searches the index, rather than the actual files on your hard drive. This is what makes it very fast in finding the info you are searching for. Unfortunately, that index itself can get out of date or corrupted, or can be deleted by mistake when restoring a hard drive, for example. Luckily, there are two ways to reindex, or rebuild, Spotlight’s database.