The act of wearing the clothes normally meant for the
sex you're not.
What is considered cross-dressing is a question of culture. The opinions on which clothing is deemed appropriate for men and women differ all over the world, and have changed over the times. Half a century ago, in Western countries, a woman wearing trousers was considered to be cross-dressing. In China trousers used to be strictly for women only. In the Middle East men routinely wear dresses...