Did anyone else read that as "What's a quid?" ?

You would generally use a GUID when you need a unique string to represent 'something' in your application. Its applications are... limitless. As an example, I wrote a file service that accepts files and stores it... a content delivery system, if you will.

Thing is, I can't store the file to disk as is. So each file name needs to be unique. Two people could upload the same file name. I could append the current datetime but that doesn't stop two people from uploading "resume.doc" at the same time. For that purpose, there's the GUID - it's a generated string which is thought to be sufficiently unique in its range to be considered truly random and unique.

Because there are 2128 possible combinations, you can let your application believe that the string generated will be unique.

In and of itself,

75B22630-668E-11CF-A6D9-00AA0062CE6C

means nothing. It is just a reference, or a key, to a certain piece of data you may have stored somewhere.