In mathematics, a tensor is an algebraic object that describes a (multilinear) relationship between sets of algebraic objects related to a vector space. Objects that tensors may map between include vectors and scalars, and even other tensors.
A tensor is a generalization of a vector (not a matrix, exactly). ... A vector is a tuple that obeys the correct transformation laws - for example, if you perform a rotation represented by matrix R, the new vector V' = RV. A tensor is a generalization of this to more dimensions.
X can be a tensor of information, an n-dimensional matrix.