The Google Design Sprint is a design thinking process done in 5 days. Each day has it's own focus (understand, sketch, decide, prototype and test). It's like a recipe you can follow to go from zero to one with an idea or concept. You could say it isn't a process by definition, but the fact that this way of working is so popular today makes it a great addition to the list of processes that inspire the Service Design work. 

The one thing I find particularly interesting with the design sprint is it's recipe format. The recipe described in the book about the process has a lot of details. It tells you which activity to do on which day, in which order and for how long. There are dozens of templates online you can find that help make it possible for you to "just" fill in the gaps and you'll get to a result at the end. The quality of this process is that it is pretty descriptive and leaves no room for interpretation where other processes give you the big building blocks but then ask you to find what is the best way to get there within each building block.

The other thing I particularly like about this design process is it's condensed nature. You know it's gonna need 5 days and you'll have a result at the end. It's a promise that you can make and one that you'll honor. So following this process can be pretty reassuring when you are new in the Service Design space as it ensures that your project won't take months and months with an unclear result.

The last thing I found fascinating with this process is the nearly "cult like" community that it has. Because there are so many fans out there of this process, you can find tons of templates, video tutorials, examples, tools, apps, and so on. It's one of the design and innovation process that has the best, richest and most diverse documentation out there.

I found the first illustration of the process on the Design Sprint LTD website. Design Sprint LTD and its founder Steph Cruchon are one of they key players in the Design Sprint space here in Switzerland. Thanks to Steph who sent me a special version of the illustration on white background. Really appreciate it!
The second illustration shown here comes from the Google Venture guide about Design Sprints.
To go much more in depth, I recommend that you read the book Sprint: "How to Solve Big Problems and Test New Ideas in Just Five Days" written by Jake Knapp, the guy who created this process. You'll find also free guides about the process on Jake's website.