Net Debit
The amount of premium paid when opening a trade where you pay more than you receive.
Explanation
A net debit represents the cost of entering a position and is the maximum loss for debit spreads. Debit trades require the underlying to move in the expected direction to profit. Time decay works against debit positions.
Example
You buy a 150/155 call spread on AAPL for a $2.00 net debit. Your maximum loss is $200 per contract.