The _dot product_ is an operation that takes two vectors in and outputs a single number (a scalar).

Here is how it works:

\$\begin{bmatrix} 1 & 2 \end{bmatrix} \cdot \begin{bmatrix} 10 & 20 \end{bmatrix} = 1 \cdot 10 + 2 \cdot 20 = 50 \$