The author re-worded iterative development where you start with a skeleton and slowly build out. Their example was to build out a simple build pipeline with stub projects that are replaced over time.
The Practice of Programming(Kernighan and Pike 1999) https://www.cs.princeton.edu/~bwk/tpop.webpage/ goes into much better details of the iterative development that is actually being done by the author. If you know the overall design of your program, you build out the skeleton with everything stubbed out. As you iterate through development, those stubs are fleshed out into fully working components.
The analogy of mise-in-enplace works if you have a ready for reusable components (COTS, FOSS, or personal) that you quickly pull off the shelf and combine into the larger product. Mise means having everything ready to go; you have your set of reusable components and subsystems that you can quickly pull together to make a new product.