The AS/400 / iSeries / i5 has had a number of names over the years.
It started life as the Application System/400 ... or AS/400.
Around the year 2000, IBM changed it's name to eServer iSeries (The "i" indicating "Integrated"?)
Then, in 2004, the name was changed to i5. The "5" referring to the Power5 Processor that was at the heart of the system. At the same time OS/400 was renamed to i5/OS.
Confused? I sure am.