Think of it that way: - JVM: Java Virtual Machine. The program that interpretes Java bytecode stored in .class files. In Windows, java.exe. - JRE: Java Runtime Environment. A JVM is not enough. You need an implementation of the core Java APIs. As you need in C the shared libraries installed in your system.
In short: JRE = JVM + core Java APIs (in jar format) + utils
The above postings are right !. Additionally if you are looking for java development, you need to download Java SDK (or called JDK ). This includes all the above and the tools to develop; compile ; debug and deploy