Update – December 17, 2014
Thanks to a PTF there is now a much easier way to use the ALIAS names in your RPG programs than the way described below.
Read Using aliases can be simple.

The ALIAS keyword in DDS has been around for many, many years. I first used it in a programming environment where most of other the programmers used Cobol. They explained that if I added a ALIAS keyword to any files I created then they could use the longer alias name rather than the field name. I have to admit that the ability to use a field or variable name that was longer than six characters greatly appealed to me. This was the days of RPGIII and I had to deal with field names like J4UEEC for "End user currency", rather than the alias END-USER-CURRENCY that the Cobol programmers could use (you have to use the underscore in the alias name and the Cobol compiler translate it to a dash). The other thing I was jealous of the Cobol programmers was the Data division being the only place to define program variables.