Debit spread
In finance, a debit spread, a.k.a. net debit spread, results when an investor simultaneously buys an option with a higher premium and sells an option with a lower premium. The investor is said to be a net buyer and expects the premiums of the two options (the options spread) to widen. Bullish & Bearish Debit Spreads

Investors want debit spreads to widen for profit. A bullish debit spread can be constructed using calls. See bull call spread. A bearish debit spread can be constructed using puts. See bear put spread. A bull-bear phase spread can be constructed using near month call & put. Breakeven Point
Breakeven for call spreads = lower strike + net premium
Breakeven for put spreads = higher strike - net premium

Maximum Potential
The maximum gain and loss potential are the same for call and put debit spreads. Note that net debit = difference in premiums. Maximum Gain
Maximum gain = difference in strike prices - net debit, realized when both options are in-the-money. Maximum Loss
Maximum loss = net debit, realized when both options expire worthless. See also
Credit spread (option)

References
 

Options (finance)
Derivatives (finance)