Java development kit termed as JDK have more than one implementation of the JVM.
Java HotSpot Client VM also termed as client VM is specifically designed for the client applications. This is the Virtual machine implementation comes with JDK.It is basically designed to cut down memory footprint and also start-up. You can invoke it by appending -client at command line at the time of its launch.
Java HotSpot Server VM also termed as server VM is specifically developed to enhancing program execution speed. You can invoke it by appending -server at command line at the time of its launch.