I also know that tensors are used to define stress and strain in mechanics. A Tensor has an order. A zero order tensor is a scalar.
Numbers are scalars.
A first order tensor is a set of numbers, or an array. A second order tensor is a matrix. A 3 x 5 matrix has the dimensions 3 and 5, but is second order. A normal stress which acts in the direction away from a surface is called a tensile stress, and it has a positive value. A normal stress which acts in the direction toward a surface is called a compressive stress, and it has a negative value.