It is common knowledge that sadaqah is financial help given for Allah's sake.
Some people suggest that it is extended to include any friendly help.
From the financial angle, how is sadaqah different from zakah. It is often used interchangeably with zakah. Indeed, it is the term used to refer to zakah in the Qur'anic verse which enumerates the classes of beneficiaries of zakah. But it is more general than zakah, because zakah denotes only that part of charitable donations which a Muslim must pay as a duty. If he refrains from paying it, he incurs a grave sin.