Qantas Club Lounge is the generic term for a Qantas lounge. Business Class passengers and Qantas Club members are invited to use the Qantas Club lounge at international airports where such lounges exist. Consequently, they are also known as the Business Class lounge. One and the same thing.
At some locations, Qantas also have a dedicated First Class lounge, where they invite first class passengers and OneWorld Emerald passengers to visit. These are known as First Class Lounges and exist at the following locations (from my head, so may be more):
Sydney, Melbourne, Brisbane, London Heathrow Terminal 4, Los Angeles Terminal 4, Singapore, Hong Kong, Bangkok (to be opening in April). At some locations they have arrangements with local lounges for their Qantas Club and Business Class passengers to one lounge and for their first class passengers to use another (e.g. SFO).
So when talking about an international terminal, Qantas Club = Business Class Lounge. First Class Lounge is separate and for first class and OneWorld Emerald passengers.