In a representative democracy, one can reasonably expect to have a parliament that is roughly representative of the population in general: poor people should have their representatives or delegates just like rich people, women just like men, minorities just like majorities. This representativity or representativeness isn’t an absolute requirement. One can have a democracy without it. The people, after all, may decide that their views are best represented by an all-male, all-white body of parliamentarians for example.
However, it seems statistically unlikely that this would be their decision in each consecutive election in each democratic country. Imbalances in the demographics of parliament that persist over time and space are probably not the result of the choices of voters but of other factors, such as discrimination, unequal opportunities etc. If that’s the case, we are dealing with an imperfect democracy because democracy means equal influence and an equal chance to get elected (art. 21 of the Universal Declaration and art. 25 of the International Covenant on Civil and Political Rights).
And that is the case. Take the share of women in parliament for instance. In almost every major democracy of the world, election after election, women are a (tiny) minority in parliament. It’s very unlikely if not impossible that women are systematically less competent than men to serve in parliament, or that the voters sincerely, rationally and objectively believe this to be the case. There must be other, more deeply embedded psychological motives for such a choice, related to the generally inferior position of women in patriarchal societies.