SplineDegree->d specifies the polynomial basis of maximal degree d in each dimension.
SplineDegree->{d1, d2, ...} specifies maximal degree dn in the ndimension.
With the setting SplineDegree->Automatic, the degree of the polynomial basis is determined from the number of control points, and the length of any knot sequence given. The default is degree 3 in each dimension.