Domain is a word which have two different meanings in 
Information technology, 

The meaning what we are taking is depends on that time only

Domain1: On what doaman we are working like java,c,c++ or 
oracle etc.,

Doman2:  on what project we are working like aircrafts 
project, banking project, tele communicatins project

these banking project is finanacial domain, on what clause 
the bank is functioned

etc