The binary operation that returns a vector of which the length and direction are those of the diagonal of the parallelogram found by using the two vectors for the sides, i.e. to add vectors p and q shown below, if $\overrightarrow{OA}=p=\overrightarrow{CB}$ and $\overrightarrow{OC}=q=\overrightarrow{AB}$ then the vector $p+q=\overrightarrow{OB}.$

The vector sum p + q