Treason is the crime of betraying your own country — helping its enemies, passing secrets to them, or trying to overthrow the government by force. It is not simply disagreeing with the government or hating it; in most countries the law asks for a real act of help to an enemy or a real attempt to bring the state down. That narrowness matters, because treason has always been the heaviest charge a state can bring: for centuries it carried death, and in some countries it still can. In Britain there is also the older phrase 'high treason', which meant betraying the monarch. Outside the courtroom, people use the word much more loosely and often half-jokingly, for any deep disloyalty to a group you belong to — 'Supporting the other team? That's treason in this house.' You can hear the difference at once: the legal use is cold and serious, the everyday use is warm and exaggerated. Note that treason is uncountable — 'he was charged with treason', never 'a treason'.