Double Threshold Mechanism
without knowing the context, it could be a number of things but one does not threshold unless you are making a decision (like a hypothesis test).

One example of a double threshold is getting through security at an airport. You go through the metal detector. The machine alerts or doesn’t . That is the first decision. It has a high false alarm rate because the cost of a missed detection is high. It alerts and you empty your pockets (hoping no one is stealing your laptop) and the machine still alerts.  The pat down is the second decision.  The pat down takes longer and has a higher cost but is usually more accurate, unless the gate is run by perverts, but that is something else. 

There are usually more thresholds that you need to pass at the airport, but the general idea of using multiple “independent “ tests to achieve better classification performance holds.