呵呵，在证券投资学里套利的概念是说投资人利用市场的缺陷发现采用无风险的手段就可以取得无风险利润的方法。

这和卖空买空时没关系。在市场里套利是对市场有力的因为这会促使市场价格的统一。

sorry for only capable to answer you with my poor english, cause I DO only have english input in my office.

which you meaned, "低位买进,高位卖空", is ONE 100% correct example.But Arbitrage means much more.

Academically, arbitrage means a transaction without negative temporal cash flow but with positive futural cash flow.And I would like explain in 3 kinds normally for the financial market:

1.different price: "低位买进,高位卖空" at the same time
e.g. you credit in japan and deposit in USA, than you have a arbitrage for the interest.
2.free lottery : without temporal pay, but possible income in the future
3.free lunch : with a zero cash flow today, but non-zero cash in the future

Practically in the market, e.g. financial market, if 2 products have different price, or cash flow structure, or volatility, or duration, or market information, or limitation etc., is the arbitrage possible.

And there are many categories of arbitrage, such like merger arbitrage, convertible bond arbitrage, regulatory arbitrage, or tringle arbitrage, or even volatility arbitrage, etc.