In law, treason is criminal disloyalty to the state. It is a crime that covers some of the more extreme acts against one's nation or sovereign. This usually includes things such as participating in a war against one's native country, attempting to overthrow its government, spying on its military, its diplomats, or its secret services for a hostile and foreign power, or attempting to kill its head of state. A person who commits treason is known in law as a traitor.
Historically, in common law countries, treason also covered the murder of specific social superiors, such as the murder of a husband by his wife or that of a master by his servant. Treason against the king was known as high treason and treason against a lesser superior was petty treason. As jurisdictions around the world abolished petty treason, "treason" came to refer to what was historically known as high treason.
At times, the term traitor has been used as a political epithet, regardless of any verifiable treasonable action. In a civil war or insurrection, the winners may deem the losers to be traitors. Likewise the term traitor is used in heated political discussion – typically as a slur against political dissidents, or against officials in power who are perceived as failing to act in the best interest of their constituents. In certain cases, as with the Dolchstoßlegende (Stab-in-the-back myth), the accusation of treason towards a large group of people can be a unifying political message. Treason is considered to be different and on many occasions a separate charge from "treasonable felony" in many parts of the world.
depicting Václav Bělský (1818–1878), Mayor of Prague
from 1863 until 1867, in charge of the city during Prussian
occupation in July 1866. Some forces wanted to try him for high treason (left: "What some men wished" – "Dr. Bělský for high treason"), but he got a full confidence from the Council of Prague (right: "but what they did not expect" – "address of confidence from the city of Prague").
In English law, high treason was punishable by being hanged, drawn and quartered (men) or burnt at the stake (women), although beheading could be substituted by royal command (usually for royalty and nobility). Those penalties were abolished in 1814, 1790 and 1973 respectively. The penalty was used by later monarchs against people who could reasonably be called traitors. Many of them would now just be considered dissidents.
The words "treason" and "traitor" are derived from the Latin tradere, to deliver or hand over.
Christian theology and political thinking until after the Enlightenment considered treason and blasphemy as synonymous, as it challenged both the state and the will of God. Kings were considered chosen by God, and to betray one's country was to do the work of Satan.
Many nations' laws mention various types of treason. "Crimes Related to Insurrection" is the internal treason, and may include a coup d'état. "Crimes Related to Foreign Aggression" is the treason of cooperating with foreign aggression positively regardless of the national inside and outside. "Crimes Related to inducement of Foreign Aggression" is the crime of communicating with aliens secretly to cause foreign aggression or menace. Depending on a country, conspiracy is added to these.