Many mathematical structures called "tensors" are tensor fields. These include scalars, spinors, tensors and spinor-tensors. Every tensor can be expressed as a sum of simple tensors. More generally, given two tensors (multidimensional arrays of numbers), their outer product is a tensor. What characterizes spinors and distinguishes them from geometric vectors and other tensors is subtle. There are several operations on tensors that again produce a tensor. Important examples of such tensors include symmetric and antisymmetric tensors. NMF extends beyond matrices to tensors of arbitrary order. For symmetric tensors these definitions are reduced. Furthermore, mixed invariants between pairs of rank two tensors may also be defined. Maxwell's equations in the language of tensors makes Lorentz covariance clear. This motivates viewing multilinear maps as the intrinsic objects underlying tensors. Laplace operator formula 189 leaves the indices symmetry of tensors. There are many examples of symmetric tensors. The values of gravitational gradient tensors are calculated and analyzed.