what is surplus?

'Surplus' in Demand and Supply issue means the supply is bigger than the demand. Hence, an excess of supply, surplus is resulted. This scenario will trigger the drop in price as supply>demand. Moreover, the supplier will adjust the production of it to make it in balance and also make the price remains stable and thus his profit is much steady. A price adjustment or balancing mechanism.
A surplus may means a positive word depending from the angle you look at it. For example, if we say the government budget is in surplus, we means the reserves has become bigger. The government has more money to spend with. So there is a room for the government to reduce tax, other levies for the purposes to reduce its income. This will give peoples more money to spend with. This will trigger a slight boom in consumer market, a higher savings rate and, most important of all, a happier life to the peoples as a whole.

呢個解釋得唔得?
在大多的解釋中，例如亞當斯密經營的古典經濟學主張自由市場會透過價格機制達成經濟均衡。也就是說，任何過度供應（market surplus 或 glut）會導致價格降低，這也使得供給的數量降低（因為生產與銷售商品的誘因減低），並且使需求的數量增加（因為提供消費者便宜的商品），這個機制就會自動廢除（abolish）過度供應的情形。相似地，在自由市場中，任何過度的需求（或說短缺）會導致價格增加，這會導致需求的的減低（因為消費者無力購買），並且增加供給的數量（因為生產與銷售商品的誘因升高）。如之前所說，不均衡情況（在這個例子中指的是短缺）將會消失。這個能自動消滅市場不平衡的市場，與所謂中央計畫的經濟類型可以區分開來。可以想見後者將有困難提供正確的價格，並且受困於貨品和服務的持續短缺。