Two, unless the vectors are colinear.
You may recall from high school geometry that two lines (not colinear) define a plane. This is the same thing. Most of the examples in this chapter use 2D vectors. But you can think of them as 3D vectors that lie in a plane.
The figure shows a vector w and an arbitrary vector v. For convenience in visualization, their tails start from the same point (but, of course, vectors have no position).
Also for convenience, the vector v is horizontal; but it could be at any orientation.