What is ment by a pool in this code

Question

https://code.sololearn.com/cNYuke5AgH50/?ref=app

Answer 1

A pool is a place where JVM (Java Virtual Machine) stores references to premade objects. Like in this example, this pool contains commonly used numbers (from -128 to 127)

there are different pools too

Answer 2

http://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.4

^Read that. Has everything you want to know about constant pools in Java.