In economics, scarcity refers to limitations--limited goods or services, limited time, or limited abilities to achieve the desired ends. Life would be so much easier if everything were free! Why can't I get what I want when I want it? Why does everything cost so much and take so much effort? Can't the government, or at least the college or local town, or if not that, my parents just give it to me--or at least make a law so that if I want to buy pizza, there is a pizza shop nearby that has to sell me pizza at a dollar a slice?
That you can't have everything you want the moment you want it is a fact of life. Figuring out how individuals, families, communities, and countries might best handle this to their benefit is fundamental to what economics is about.
You are probably used to thinking of natural resources such as titanium, oil, coal, gold, and diamonds as scarce. In fact, they are sometimes called "scarce resources" just to re-emphasize their limited availability. Everyone agrees natural resources are scarce because they take a lot of effort, money, time, or other resources to get, or because there seems to be a finite amount available.
But what constitutes a lot of effort, money, time, or other resources? Does it matter if something is finite if we can easily substitute something else? It all depends on your circumstances. Most people don't think of water as scarce, but if you live in a desert, water is scarce. If you are a teenager or in college, iPhones or the hottest sneakers or the recognition of your peers or a person of interest are as scarce--as difficult to acquire--as gold. If you are running out of space on your hard drive but you can substitute cloud computing, is storage space scarce?
In fact, economists view everything people want, strive for, or can't achieve effortlessly as scarce. For example,
Every time you turn on the tap and get fresh water, that fresh water is part of what economists deem as scarce. Instead of...