If the government of spain decides to spend less on the military and more on health care, the forgone spending on military items represents the:

I believe the answer is: opportunity cost of the extra health care

Opportunity cost refers to the options that we ma have to abandon in order to choose another option. Both health care and military spending come from the same federal budget. So, if government choose to allocate it to health care, they need to abandon the plan to purchase some of the things for military,