Cake is a cross-platform build automation system that uses a C# DSL to compile code, copy files, run unit tests, compress files, and build NuGet packages. It uses a C# script file called a Cake file to define and orchestrate build tasks like clean, build, unit tests, test coverage, static analysis, versioning, packaging, and publishing. Cake is executed by Cake.exe and supports building outputs like NuGet packages, EXEs, DLLs, and MSIs.