ahead of time (AOT) compilation is the act of compiling a higher level programming language

In computer science, ahead-of-time (AOT) compilation is the act of compiling a higher-level programming language such as C or C++, or an intermediate representation such as Java bytecode or .NET Framework Common Intermediate Language (CIL) code, into a native (system-dependent) machine code so that the resulting binary.Wiki Link for the same: https://en.wikipedia.org/wiki/Ahead-of-time_compilation

Ahead-of-Time (AOT), it compiles angular app at build time. It converts your Angular HTML and TypeScript code into efficient JavaScript code during the build phase before the browser downloads and runs that code.

Aot compilation is used to convert the html code into efficient javascript code

Angular's Ahead-of-Time (AoT) compilation is a powerful tool, that improves page load by such multiples that speed-up is sensible by human beings. In our case, an application bundled with the AoT compiler loads 3 times faster than the same application bundled with the JiT compiler.