MUI.nsh vs. System.nsh

I've been looking through some NSIS script examples, and noticed that sometimes "MUI.nsh" is defined, and sometimes "System.nsh" is defined. What's the difference between these??? Thanks in advance!!

There is none. System.nsh is only used in old examples. MUI.nsh is a lot easier to include because it doesn't require the whole path to be included, just a simple !include MUI.nsh.