Final answer:
When the DMM reading is less than zero, it means the voltage being measured is negative.
Step-by-step explanation:
When Vero puts the probe of her DMM across two terminals to check the voltage and notices that the reading is less than zero, it means that the voltage she is measuring is negative. In electrical circuits, voltage can be both positive and negative.
A negative voltage reading indicates that the voltage is in the opposite direction to the reference point or the ground.