A substance through which an electrical current flows poorly would be said to be a poor conductor. That is, the substance has a low conductance (or conductivity). There’s a nuance between the two terms, but it shouldn’t matter for our purposes.
Since such a material resists the flow of electric charge, the material can be said to have a high resistance (or high resistivity).
Mathematically, resistance and conductance are reciprocals of one another; a low conductance implies a high resistance, and a high conductance implies a low resistance.