Delta Fare class Z is a revenue fare/booking class of service that is marketed as Discount First Class / Delta One on Delta Air Lines. The fare class is considered a discounted First Class / Delta One.
Fare class Z is a business fare tier on many airlines. F or J is the top tier (F means/meant First Class; most airlines don't use this class name any longer.) Z is a discounted business class fare tier. Still pricey, but less than paying F or J fares.
The main difference between economy and business classes lies in the prices and facilities offered. The fare of a business class is two to five times higher than an economy class. The business class allows you to carry additional luggage. Plus, you get free food and drinks, lounge services, and wider seats.
You'll usually find business class seats in the fancy part of the plane, behind first class, but still separated from economy/premium economy by a curtain. In some cases, they're the most expensive cabin class available, so they'll be at the front-most cabin or upper deck of the aircraft.
The economy class is used in the same way all around the world. To get the cheapest prices, travelers usually book economy class tickets in advance. As economy class tickets are high-demand tickets, you might want to book it in advance to freeze the price in case the price increases.
Economy Class is the third-tier or the lowest class in aeroplane travel. Some call it coach, while others call it cattle class, but it is the basic class. The seats are less spacious. The ticket prices are cheaper than the other classes. Economy class is different on different flights depending on the airline.