[IanCal]

You are right this is ML 101, but you are wrong. Someone else has linked the wiki page, and I've posted it elsewhere and I would strongly recommend you read it as your interpretation is very incorrect.

> In English, a false positive is when the machine declares something as positive but it is actually negative.

Yes, and the rate is based on the frequency this happens in your negative set.

>This fits a sanity test because ~50% of people that pass through a detector do not get patted down.

The 50% figure may be wrong, but my definition of what a false positive rate is not.