Question: Can someone explain the differences between GraalVM and Jvm-Hotspot, and how GraalVM is related to OpenJDK's HotSpot.

Answer: 
GraalVM is a JVM with multiple change:

* the graal compiler. It is intended to replace the C2 compiler (server mode) in front of HotSpot.
* Truffle a library that you can implements to make JVM polyglot ( there already a number of language that are supported like js, R, Ruby...)

The graal project also have a Substrate VM which is a framework to build native artifact from Java.
Detailed information about how Graalvm performs better than standard Hotspot and how to use it: <https://www.baeldung.com/graal-java-jit-compiler>