The answer is metamorphic rock.
The picture attached is the diagram you are referring to.
Metamorphic rocks form from existing rock. It is due to heat and pressure that these types of rocks are formed. They don't melt into magma but the heat and pressure change the chemical structure of the rocks. This is why there is no arrow that points to magma, unlike the other two types of rocks. They can be broken down and form into sedimentary rocks.