Linearly interpolates between two vectors.
Interpolates between the vectors a and b by the interpolant t. This is most commonly used to find a point some fraction of the way along a line between two endpoints (e.g. to move an object gradually between those points).
When t = 0 returns a.
When t = 1 returns b.
When t = 0.5 returns the point midway between a and b.
Additional resources: Lerp.