Flawless articulation

I’ve never tried to define an arrow before, but this website explaining vector notation nailed it.

Many quantities in geometry and physics, such as area, time, and temperature, can be represented by a single real number.  Other quantities, such as force and velocity, involve both magnitude and direction and cannot be completely characterized by a single real number.  To represent such a quantity, we use a directed line segment (arrow) called a VECTOR.