Final answer:
The coefficient of the first term in the expression -12m + 8n is -12, and it's crucial to include the sign when identifying it.
Step-by-step explanation:
The coefficient in the mathematical expression -12m + 8n refers to the numerical factor that is multiplied by the variable. In this expression, the first term is -12m, so the coefficient is -12. It is important to include the sign when identifying the coefficient, as this denotes whether the term is positive or negative in the context of the expression.