A plain-language explanation
Java is an object-oriented programming language and runtime platform used, among others, in business systems, server applications and mobile solutions.
Where it helps in practice
Java is a language and platform used in many backend systems and should not be confused with browser-side JavaScript.
The decision before implementation
Choose it for architecture, team capability, performance needs and maintenance lifecycle rather than popularity alone.
How to verify the result
Track runtime versions, dependencies, tests, resource use and security updates throughout the application lifecycle.