Tari was a nation from thousands of years ago that was founded and ruled by the Console Patron Unit, Rei Ryghts. It is remembered as a nation of tyranny and despotism in old documents according to Blanc. It was a nation that ruled over all of Gamindustri before its destruction.
Thousands of years ago, when Rei Ryghts became a goddess and founded the nation of Tari, she at first attempted to lead the people as best as she could, but due to her tyrannical nature when she becomes powerful, the people decided to rise against her and demand freedom from her dictatorship. Rei approached the situation with her same tyrant outlook and ended up destroying her nation and its people within a matter of minutes, causing her to lose nearly all her powers as a CPU. This event was known as The Great Crash.
In the extra chapter of Hyperdimension Neptunia Re;Birth3: V Generation, Bamo and Regu found OOParts in the ruins of Tari. Those items were made to counter the despotic CPU, Rei Ryghts. However, the two of them used the parts to assist them in their plan to overthrow the CPUs to create Sociomobilindusrti.
Much like Rei, Tari is a reference to game corporation Atari.