Final answer:
Steep-sided inlets of the sea formed from flooded glacial valleys are called fjords. They are created by the erosion of valley glaciers, followed by sea level rise that floods the valley.
Step-by-step explanation:
The steep-sided inlets of the sea created when a glacial valley is flooded as sea level rises are known as fjords. These inlets are typically long, narrow, and very deep. The process begins with a valley glacier that carves a U-shaped valley by erosion. After the glacier retreats and melts, the sea can flood the valley, forming these dramatic inlets that are often characterized by their steep cliffs and deep waters.