An irreducible fraction is a fraction p/q for which GCD(p, q) = 1, i.e., p and q are relatively prime. For example, in the complex plane, (4 + 7i)/(2 + i) = 3 + 2i is reducible, while (5 + 5i)/(7 + i) = 4/5 + 3i/5 is not. The figure above shows the irreducible fractions plotted in the complex plane.

fraction | reducible fraction