A programming language I guess which is used to code Android Applications, Desktop Applications and more. Now Android applications can also be coded using Kotlin Programming.
Java Programming was initially developed and designed by Sun Microsystems initiated by James Gosling and released in 1995 as a core component of Sun Microsystems' Java platform.
It is guaranteed to be Write Once and, Run Anywhere. You can find my answer in Youth4Work on how you can learn Java here https://www.prep.youth4work.com/Practice-Tests/Programming-in-Java-Test/Forum/22962/Answer/45795
Another thing is sources, where you should start with to learn java there are many good channels which provide good knowledge of Java such as the new Boston my personal favorite from where I have learned, java point website is also good as a learning source finally if you encountered any problem you can ask it on stackoverflow