A simple model of two dimensional electrically anisotropic sample is used to explain the content of the term tensor and its usefulness. In anisotropic solids the vector of current density doesn´t need to be parallel to the electric field intensity vector. Therefore the relation between these vectors is not a simple scalar multiplication, but an algebraically more complicated relation is needed, mediated by tensor. In the article the connection between matrix and tensor formulation is mentioned, the tensor form in three dimensional cartesian coordinate system and for illustration the tensor characterizing optical properties of muscovite is presented. The article contains also the citation of the basic tensor literature.