A simple doubt.....

An offshore bank is a bank located outside the country of residence of the depositor, typically in a low tax jurisdiction (or tax haven) that provides financial and legal advantages. 

for more read

https://en.wikipedia.org/wiki/Offshore_bank

Offshore banking unit (OBU) is the branch of an Indian bank located in a special economic zone (SEZ), with a special set of rules aimed at facilitating exports from the region. As laws define it, it's a "deemed foreign branch" of the parent bank situated within India, and it undertakes international banking business involving foreign currency denominated assets and liabilities. The concept comes from the practice prevalent in several global financial centres. Here an OBU can accept foreign currency for business but not domestic deposits from local residents. This was conceived to prevent competition between local and offshore banking sectors.