What type of coastline is characterized by rock outcrops at right angles to the sea, forming headlands and bays?

A coastline characterized by rock outcrops at right angles to the sea, which forms headlands and bays, is known as a discordant coastline. This type of coastline consists of alternating layers of hard and soft rock that erode at different rates. The harder rocks form prominent headlands, while the softer rocks erode more quickly, leading to the formation of bays.

In contrast, concordant coastlines have rock layers that run parallel to the sea, resulting in more uniform erosion along the coast, without distinct headlands and bays. Channel coastlines refer to narrow bodies of water between coastlines and are not specifically a type of geological formation like the others. Estuarine coastlines are found where rivers meet the sea, often characterized by varying salinity and sediment deposition rather than the distinctive structure of headlands and bays created by differential erosion. Thus, the defining feature of headlands and bays in this question supports the classification as a discordant coastline.