There are at least two bands called ZAO, the first of which are still active, the latter haven't done anything since 1994:
1) Zao (pronounced /ˈzeɪ.oʊ/) is a band from Greensburg, Pennsylvania and are considered one of the founding metalcore groups. However they began in 1993 in Parkersburg, West Virginia, playing a style of Hardcore similar to bands such as Earth Crisis and Snapcase. Zao has hosted several musicians and endured numerous roster changes to the point where no original members remain, often marked by the departure and readmission of multiple members. The band's catalog is often divided into two distinct eras, marked by a drastic shift in members that led to an equally drastic shift in sound. Most noticeably of these changes was the shift from vocalist Shaun Jonas who later formed Symphony in Peril to current front-man Dan Weyandt. Throughout the years, Zao has hosted many notable musicians such as guitarist Brett Detar of The Juliana Theory fame and current drummer Jeff Gretz who briefly played for From Autumn to Ashes. In the eyes of many fans, the "core" of Zao's sound was best exemplified by drummer Jesse Smith, guitarists Russ Cogdell and Scott Mellinger(formerly of Creation is Crucifixion), and vocalist Dan Weyandt. The current lineup is comprised of Russ, Scott, Dan, Jeff, and bass player and long time friend of the band, Martin Lunn.
To date, Zao has completed ten full-length albums, three EPs, a two-disc DVD documentary and multiple concert tours, garnering a limited but global fanbase and earning critical praise in the process.
2) ZAO was a French zeuhl band, an early Magma offshoot. If one regards MAGMA as the central trunk of the Zeuhl tree, ZAO would be equivalent to an early side branch very close to the stock. ZAO’s music, at least at the beginning of their career, is therefore an extension of MAGMA’s first era, with a light music, at times weird, with hints of jazz, contemporaneous music, Hungarian folk (Yochk’o is a native of Hungary) and obviously of Zeuhl. Nothing in common with the absolute incantatory power of “MDK” and “Kohntarkhosz” to which Yochk’o Seffer and François Cahen didn’t want to contribute.
In the first album, "Z = 7L" (1973), the very complex melodic instrumental layers are enriched with the wonderful voice of Mauricia Platon (with its kobaïan accents), but unfortunately she was missing on the follow-up "Osiris" released in 1975.
ZAO will break from its Zeuhl roots and the music will lean towards some jazz-rock fusion more and more debatable and debated.