Final answer:
A leftward shift of a supply curve is called a decrease in supply, indicating that at any given price, less quantity will be supplied due to factors like increased production costs.
Step-by-step explanation:
A leftward shift of the supply curve signifies a decrease in supply. This can occur due to various factors, such as an increase in costs, which makes it more expensive to produce goods. At every price level, the quantity supplied will be lower when the supply curve shifts to the left. A leftward shift is different from a 'decrease in quantity supplied', which is a movement along the supply curve due to a price change rather than a shift of the entire curve.
For example, if the cost of leather increases, then the supply for leather watches would shift to the left, depicting that at the previous prices, fewer watches can be supplied due to the higher costs involved in production.