JDK and JRE ---> Platform dependent, these are specific to different system. JVM ---> Platform independent, because JVM is specifications for JRE. It means JVM has some set of rules and JRE is giving the implementation to it. So, JRE is physical implementation of JVM.

Ex- Bank has some specific rules and SBI, BOI and UCO are the implementation for the Bank. Here in this case BANK is JVM and SBI, BOI and UCO are JRE.