Final answer:
A fully developed sea has waves that have reached their maximum potential size due to sustained winds over a large area, but wave power is unlikely to be a primary energy source.
Step-by-step explanation:
When we say a sea is fully developed, we refer to a condition where the wind has blown over a large area of water for a sufficient time period, allowing waves to reach their maximum potential size given the wind speed, duration, and fetch (the distance over which the wind blows).
These fully developed seas have large, well-formed waves that can carry considerable energy towards coastlines, where it can sometimes be harnessed to generate electricity. However, it's important to highlight that wave power, despite its potential, will unlikely become a primary energy source compared to other alternatives like solar power since it represents only a small fraction of global energy demand and has significant ecosystem impacts.