It is the projection length from one vector A to another vector B multiplied by the length of vector B, and the projection result is positive in the same direction and negative in the opposite direction. When orthogonal, the projection length is 0, so the result is 0.

In mathematics, vectors (also known as Euclid)

Vector, geometric vector, vector) refers to a quantity with magnitude and direction. It can be imagined as a line segment with an arrow. The arrow indicates the direction of the vector; Line segment length: indicates the size of the vector. The quantity corresponding to a vector is called a quantity (called a scalar in physics), and a quantity (or scalar) has only a size and no direction.