The full form of ZAO can vary depending on the context. However, based on the provided reference, one possible full form is Zonal Accounts Office.
While "Zonal Accounts Office" is one possible full form, especially in contexts related to field pay units, it is important to note that ZAO may have other meanings in different contexts. Without further context, it's difficult to definitively say that "Zonal Accounts Office" is the single, correct answer.
Other potential meanings (although not supported by the provided reference) could include acronyms related to organizations or legal entities in different countries.
Therefore, the answer derived from the provided source is:
- ZAO: Zonal Accounts Office
