Formula Front is the worldwide phenomenon in which unmanned, AI-controlled ACs (u/ACs) are pitted against one another in fiercely contested arena battles.
The player assumes the role of an "Architect". An Architect is a person who builds, programs and battles with a modified Armored Core known as a "u/AC" or an Unmanned Armored Core. u/ACs are AI controlled Armored Cores which compete exclusively in battling tournaments. u/ACs battle independent of the Architect's control, so the Architect must influence how the u/AC fights by customizing various part combinations and loading various program functions into the u/AC's AI.
Source: Wikipedia, "Armored Core: Formula Front", available under the CC-BY-SA License.