Mercy (Middle English, from Anglo-French merci, from Medieval Latin merced-, merces, from Latin, "price paid, wages", from merc-, merx "merchandise") can refer both to compassionate behaviour on the part of those in power (e.g. mercy shown by a judge toward a convict) or on the part of a humanitarian third party (e.g. a mission of mercy aiming to treat war victims). Mercy is a term used to describe the leniency compassion shown by one person to another, or a request from one person to another to be shown such leniency or unwarranted compassion for a crime or wrongdoing. One of the basic virtues of chivalry, Christian ethics, Judaism, and Islam, it is also related to concepts of justice and morality in behaviour between people. In India, compassion is known as karuna.
To be "mercy", the behavior generally can not be compelled by outside forces. (A famous literary example is from The Merchant of Venice when Portia asks Shylock to show mercy. He asks, On what compulsion, must I? She responds The quality of mercy is not strained.)