This is a spread where the premium received from selling part of the spread is greater than the premium paid for the other part of the spread.
For instance, if you sold the AAPL 140.00 Calls @ 4.00 and bought the AAPL 142.00 Calls for 2.00 you have a credit of 2.00.
See also Bear Call Spread, Bear Put Spread, Calendar Spread etc
