Final answer:
A component of a vector represents a piece of the vector that points in either the x or y direction. The component dy of vector d is the vertical part of the vector.
Step-by-step explanation:
A component of a vector is a piece of the vector that points in either the x or y direction. For a two-dimensional vector, the component can be expressed as a sum of its x and y components. In the context of your question, the component dy of vector d represents the vertical part of the vector.