To quote from Wikipedia:
Java is a general-purpose computer programming language that is concurrent, class-based, object-oriented,and specifically designed to have as few implementation dependencies as possible. It is intended to let application developers “write once, run anywhere” (WORA).
To state in a layman’s terms, Java is the language of applications. To put things into context, a majority of the applications currently in your phone would have been developed using Java. It is a strongly typed language which is quite serious about its syntax which is similar to oldies like C and C++. It’s like that old grandpa to whom you go with your generic life problems to get a solution with his experience, who once upon a time was inevitable to the world, and hence has a major experience, legacy, and fan following.