Impulse Purchase:

An impulse purchase or impulse buy is an unplanned or otherwise spontaneous purchase. One who tends to make such purchases is referred to as an impulse purchaser or impulse buyer.
Marketers and retailers tend to exploit these impulses which are tied to the basic want for instant gratification. For example, a shopper in a supermarket might not specifically be shopping for confectionary. However, candy, gum, mints and chocolate are prominently displayed at the checkout aisles to trigger impulse buyers to buy what they might not have otherwise considered. Alternatively, impulse buying can occur when a potential consumer spots something related to a product that stirs a particular passion in them, such as seeing a certain country's flag on the cover of a certain DVD. Sale items are displayed in much the same fashion.
Impulse buying can also extend to so-called "big ticket" items such as automobiles and home appliances. Automobiles in particular are as much an emotional purchase as a rational one. This in turn leads auto dealers all over the world to market their products in a rapid-fire, almost carnival-like manner designed to appeal to emotion over reason.
Impulse buying disrupts the normal decision making models in consumers' brains. The logical sequence of the consumers' actions is replaced with an irrational moment of self gratification. Impulse items appeal to the emotional side of consumers. Some items bought on impulse are not considered functional or necessary in the consumers' lives. Preventing impulse buying involves techniques such as setting budgets before shopping and taking time out before the purchase is made.