A call debit spread is also referred to as a bull call debit spread, debit spread or a long call spread. It is a multi-leg options strategy comprised of one long call and one short call option at a higher strike price in the same stock and the same expiration. It's a strategy used when you're bullish on the underlying stock. It's a debit trade because you pay for the trade rather than receive a premium payment like in a credit spread.
Debit spreads usually comprise an in-the-money (ITM) long call and an out-of-the-money (OTM) short call. However, you can have an OTM long call and even more OTM short call. The short call should have a higher strike price than the long call, which helps to finance part of the long call. The remaining cost is the price you pay for the trade. Debit spreads are ideal when implied volatility is low (IV) as it starts to rise.