What is a "Walking Skeleton"?
A "Walking Skeleton" is a form of "proof of concept" of your basic architectural concept. Where a proof of concept typically focuses more on a single functionality, a "Walking Skeleton" is a minimalistic end-to-end implementation. A "Walking Skeleton" is not an outline of your concept (only a "skeleton") but is really executable and shippable (it can "walk" :O) and should be accompanied with tests.

Alistair Cockburn has described it (and is being quoted often):  


  A Walking Skeleton is a tiny implementation of the system that performs a small end-to-end function. It need not use the final architecture, but it should link together the main architectural components. The architecture and the functionality can then evolve in parallel.


The advantage here for DevOps is that a "Walking Skeleton" should be developed early on in the project and results in working, shippable and testable code. This way DevOps can set up a full continuous integration chain early in the project, instead of being onboarded in the final phase of projects. This means that any issues that would arise are also being tackled in an early stage instead of rush work at the end.