<reference no-default-lib="true"/>

/// <reference no-default-lib="true"/>

This directive marks a file as a default library. You will see this comment at the top of lib.d.ts and its different variants.

This directive instructs the compiler to not include the default library (i.e. lib.d.ts) in the compilation. The impact here is similar to passing --noLib on the command line.

Also note that when passing --skipDefaultLibCheck, the compiler will only skip checking files with /// <reference no-default-lib="true"/>.