From ACT Wiki
A composite speculative deal in two options, which results in a profit/loss profile similar to a conventional call option, except that the upside potential is capped in return for a reduction in the net premium payable.
A bull spread can be constructed using call options by buying a call with a given strike price, and selling an otherwise identical call with a higher strike price. It can also be constructed using appropriate put options.
Sometimes known as a 'risk reversal'.