For Economy Class, the checked baggage allowance is usually one bag weighing up to 23kg (50lbs). For Business Class, it's two bags up to 23kg each, and for First Class, it's three bags up to 23kg each.
In addition to the checked baggage allowance, passengers are also allowed to carry one piece of hand luggage on board, weighing up to 7kg (15lbs) and measuring no larger than 56cm x 36cm x 23cm (22in x 14in x 9in).
For more specific information about baggage limits on your particular flight, it's best to check with Etihad Airways directly.