Gundam Wiki:Timelines

There are many timelines in the Gundam universe.

Universal Century
Universal Century is the English name for the original timeline of the Gundam anime metaseries. It is also called "Uchuu Seiki", meaning "The Era of Space", in Japanese, but the official English name Universal Century is always used to tag along the Japanese kanji name and is often abbreviated as "UC".

The Universal Century universe remains by far the most developed one, with four TV series, four OVA series, fifteen theatrical releases, and various specials.

Future Century
Future Century is an alternate timeline. It is often abbreviated as "F.C."

After Colony
After Colony is an alternate timeline corresponding to the construction of the first space colony in Earth orbit. It is often abbreviated as "AC" The After Colony timeline differs from the Universal Century in that an Earth Federation-like government, (The Earth Sphere Alliance and later the Organization of the Zodiac), retains control of the space colonies and is more oppressive. The colonies struggled for freedom, and the Gundams were built as way of defending the plight of the colonies to escape this oppression.

The After Colony universe is the third most developed, with one TV series, one OVA series and a compilation movie.

After War
After War is an alternate timeline noted for its distinct apocalyptic world. However, it has many similarities with the Universal Century. After War is the only timeline, besides the U.C., to feature Newtypes as an important element.

Correct Century
The Correct Century is known as Seireki in Japanese. Seireki is a wordplay on the Japanese term for the Common Era (C.E.) Western calendar system (西暦; also pronounced Seireki). Its kanji literally means "Correct Calendar" and is unofficially interpreted as "Correct Century" by English-speaking fans.

Cosmic Era
Cosmic Era is an alternate timeline. It is often abbreviated as "C.E."

The Cosmic Era universe is the only Gundam universe after the original Universal Century with multiple TV series. It is also the second most developed, with two TV series, one ONA and two compilation movies.