Unity (Jumbo) builds are a way to increase speed compilation for C/C++ projects. The following [article: A guide to unity builds](http://onqtam.com/programming/2018-07-07-unity-builds/) by Viktor Kirilov describes the concept in detail. Another article about Unity (Jumbo) builds: [Support for Unity (Jumbo) Files in Visual Studio 2017 15.8](https://devblogs.microsoft.com/cppblog/support-for-unity-jumbo-files-in-visual-studio-2017-15-8-experimental/). See also the discussion on Google Chromium mailing list: [Using unity builds (jumbo) for Chromium](https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/ThDAjO7fTro).