A way of multiplying two vectors:
a · b = |a| × |b| × cos(θ)
Where || means "the magnitude (length) of"
And θ is the angle between the vectors
Example: the lengths of two vectors are 3 and 4, and the angle between them is 60°
So the dot product is:
a · b = 3 × 4 × cos(60°) = 3 × 4 × 0.5 = 6