Final answer:
Stage 3 sleep is the sleep stage characterized by low frequency, high amplitude delta waves, making it difficult to wake a person from this deep sleep.
Step-by-step explanation:
The stage of sleep characterized by delta waves, which are very high amplitude and very low frequency brain waves, is Stage 3 sleep. These delta waves have the lowest frequency, less than 3 Hz, and the highest amplitude of our sleeping brain wave patterns.
During Stage 3 sleep, also known as deep sleep or slow-wave sleep, an individual's heart rate and respiration slow down significantly, and waking the person from sleep is quite difficult.