Let $\vec{a}$ & $\vec{b}$ be two non-collinear, non-zero co-initial vectors having angle $\theta$ between them. The projection of $\vec{b}$ on $\vec{a}$ is given by the dot product of $\vec{b}$ &$\hat{a}$.
This is the mathematical definition. But what it is actually? What is the definition of it?
[ I guess it is the magnitude of component of $\vec{b}$ on $\vec{a}$.]