Yes, I know it sounds a bit oxymoronic. Either an application has a server component - distinct from the client - or it doesn't. How could an application design be both client/server and standalone thick client?
By embedding the server side component, inside the client side, you can essentially compile-away the network layer. Inside of course, all the code operates on the basis of client/server communications paradigms but all of that happens without the classic distributed computing fallacies potentially biting you. Ultimately everything network-ish is on the loopback interface.
I like this style much more than I like its mirror image, which is to design with thick client paradigms and then insert a network layer "transparently" by making the procedure calls turn into remote procedure calls.
The problems with the latter are that all the distributed computing fallacies hold and without designing for them, your application is ill-equipped to cope with them.
If we are swinging back towards a more client-side-centric UI model and I believe we are, doing it with things like, say, electron rather than going back to traditional, say Win32 + DCOM/CORBA/J2EE, makes sense now that we are all (mostly!) well familiar with the impossibilty of wishing away the network:-)