Module is a simple container of values, types definition and sub modules. There are two types of modules. Local modules and top level ones. The following video clips show how to define them. You can find the source code as part of my F# Fundamentals course. Its community version is available for free personal usage at www.abelski.com.

Stable Values in Java (JEP 502): Deferred Immutability with JVM Trust
Explore Stable Values – a new Java 25 upcoming feature (JEP 502) enabling lazy initialization with immutable performance and JVM-level optimizations.