Investment : Option

Long a call means buying a call option, while short a put means selling/writing a put option.

The difference between the two is that when you buy an option, you need to pay a premium. But when you sell, you receive a premium instead. Another differerence is that the pay-off at maturity. Buying a call gives you limited loss but unlimited gain. But when you sell a put, you maximum gain is your premium received but potential loss is the strike price.

You need to understand what are Call and Put Options first. And remember Long means buy and Short means sell. Please check out the following links for definition and example of Call and Put Options.
http://en.wikipedia.org/wiki/Call_option
http://en.wikipedia.org/wiki/Put_option