The Ahead of Time (AOT) compilation lets you convert your code during its build time before your browser downloads and runs it. This leads to faster rendering to your browser. You need to include the --aot option with the ng serve or ng build command to specify this compilation.
JIT (Just in Time) compilation, on the other hand, is the process of compiling computer to machine code during execution or run time. Also known as dynamic compilation, JIT compilation is the default function when you run ng serve or ng build CLI commands.