There is a basic economy class being talked about and even offered by some airlines. Seating is a higher density in that part of the cabin or involves getting the middle seat, limited if any baggage allowance and possibly no meal or frequent flyer points. Its a step down from regular economy in the same way that premium is a step up.
Fares reflect the lack of frills, however the frills are available on the same aircraft at a higher price. This enables full service airlines to compete with low cost carriers without setting up a separate operation. Passengers can buy the level of comfort that they are prepared to pay for and have no justification in complaining as product and price are laid out at the time of booking.
I sometimes see four levels of economy ticket available; Fully flexible, regular, saver and super promo with decreasing flexibility and increasing cost to alter the tickets as the price goes down. However the cabin and amenities are still the same.
Basic takes this a step further enabling the cost conscious to pay less for a lower standard in the cabin. A college student going home on holiday on a two hour flight would probably be quite happy with basic, a couple going on honeymoon would want a bit more and a business man would want flexibility. Everyone could be catered for by the same airline on the same aircraft.
Airlines to Introduce a New Passenger Class Below Economy - Fortune