What is the difference between Java and JavaScript?

Java

Java is a compiled, statically-typed language.

It is primarily used to write back-end (or server) applications that live in the Cloud.

Here is how you print Hello World! in Java:

public class HelloWorld {
  
  public static void main(String[] args) {
    System.out.println("Hello World!");
  }
}

JavaScript

JavaScript is an interpreted, dynamically-typed language.

It is primarily used to write front-end (or client) applications that live in the Web Browser.

Here is how you print Hello World! in JavaScript:

console.log("Hello World!");

Why their names are so similar?

In the mid 90's, Netscape added a scripting language to their Navigator (one of the first Web Browsers).

They called the language "JavaScript" to associate it with then popular Java language.

It was just a "marketing ploy" to get more attention.