The human back is the large posterior area of the human body, rising from the top of the buttocks to the back of the neck and the shoulders. It is the surface opposite to the chest, its height being defined by the vertebral column (commonly referred to as the spine or backbone) and its breadth being supported by the ribcage and shoulders. The spinal canal runs through the spine and provides nerves to the rest of the body.

The central feature of the human back is the vertebral column, specifically the length from the top of the thoracic vertebrae to the bottom of the lumbar vertebrae, which houses the spinal cord in its spinal canal, and which generally has some curvature that gives shape to the back. The ribcage extends from the spine at the top of the back (with the top of the ribcage corresponding to the T1 vertebra), more than halfway down the length of the back, leaving an area with less protection between the bottom of the ribcage and the hips. The width of the back at the top is defined by the scapula, the broad, flat bones of the shoulders.

In economics, demand is the desire to own anything, the ability to pay for it, and the willingness to pay. Basically Demand refers to how much (quantity) of a product or service is desired by buyers. The quantity demanded is the amount of a product people are willing to buy at a certain price; the relationship between price and quantity demanded is known as the demand relationship. (see also supply and demand). The term demand signifies the ability or the willingness to buy a particular commodity at a given point of time.

Economists record demand on a demand schedule and plot it on a graph as a demand curve that is usually downward sloping. The downward slope reflects the relationship between price and quantity demanded: as price decreases, quantity demanded increases. In principle, each consumer has a demand curve for any product that he or she would consider buying, and the consumer's demand curve is equal to the marginal utility (benefit) curve. When the demand curves of all consumers are added up, the result is the market demand curve for that product. If there are no externalities, the market demand curve is also equal to the social utility (benefit) curve.

Travel is the movement of people or objects (such as airplanes, boats, trains and other conveyances) between relatively distant geographical locations.

The term "travel" originates from the Old French word travail. The term also covers all the activities performed during a travel (movement). A person who travels is spelled "traveler" in the United States, and "traveller" in the United Kingdom.^{[citation needed]}

"The World is a book, and those who do not travel read only a page."

Reasons for traveling include recreation,tourism or vacationing,research travel for the gathering of information, for holiday to visit people, volunteer travel for charity, migration to begin life somewhere else, religious pilgrimages and mission trips, business travel,trade,commuting, and other reasons, such as to obtain health care or fleeing war or for the enjoyment of traveling. Travel may occur by human-powered transport such as walking or bicycling, or with vehicles, such as public transport, automobiles, trains and airplanes.