GUID - the Microsoft Flavour of UUID
A GUID is a UUID in Microsoft dress: uppercase hex and optional braces, the format expected by .NET, SQL Server and Windows APIs.
Whether GUID and UUID are actually different things (and where the naming came from) is settled in UUID vs GUID.
When to Use This Version
Use GUID format when working with Microsoft technologies: .NET applications, SQL Server databases, COM components, Active Directory, Azure services. The uppercase format and optional braces ({...}) are Windows conventions.
Best Practices
In .NET, use Guid.NewGuid() for generation. SQL Server uses NEWID() or NEWSEQUENTIALID() (for sorted inserts). For cross-platform compatibility, store as lowercase UUID internally and convert to GUID format only for Microsoft-specific interfaces.