An impulse purchase is an unplanned or otherwise spontaneous purchase. One who tends to make such purchases is referred to as an impulse buyer.
Marketers and retailers tend to exploit these impulses which are tied to the basic need for instant gratification. For example, a shopper in a supermarket might not specifically be shopping for candy. However, candy, gum and mints are prominently displayed at the checkout aisles to trigger impulse buyers to buy what they might not have otherwise considered. 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.
I've never bought a car on an impulse. LOL
Last night I went to my gardening class, and on my way out of the store, was faced with a wall of Dutch licorice candy. I love licorice, so I picked out a package, and checked out.
As I drove out of the parking lot, I popped a piece in my mouth. Whoa! That stuff was nasty! I'll try another piece. Even nastier! My mouth was burning, my sinuses were bothering me, and I was anxious to get home so I could get a drink of water. It was THEE nastiest, grossest, yuckiest, most disgusting "candy" I've ever tasted!
Now, maybe some Dutch licorice is good. However, I doubt if I'll ever find out!