“The ability of an individual or group to carry out a particular economic activity (such as making a specific product) more efficiently than another activity.” (Oxford Dictionary of English)
“The essence of this law can be illustrated with a simple example. Imagine that you are a skilled cabinetmaker as well as a gifted painter. It takes you a day to build a cabinet or a day to paint a picture. In the local economy, paintings sell for $400 and cabinets go for $350. Your neighbor also shares the same skill sets, but it takes him a day and a half to build a cabinet and three days to complete a painting. You have an absolute advantage over your neighbor in both areas, so you should try to outproduce him across the board, right? Wrong.
Here’s why: If you flip between painting and cabinetmaking over a six-day work week, you would produce three paintings and three cabinets worth $2,250. If your neighbor embarked upon the same work schedule, he would produce one painting and two cabinets worth $1,100. There would be a total of four paintings and five cabinets produced: a total of nine production units. If, however, you were to choose to focus on painting, the area where you have the greatest comparative advantage and the most profit, and leave cabinetmaking to your neighbor, something magical would happen. You would produce six paintings worth $2,400 per week, while your neighbor would produce four cabinets worth $1,400, bringing the total to 10 production units. In real terms, both you and your neighbor would be richer for specializing – and the local economy is one production unit the better for it.” (Investopedia)