What is the definition of a charitable endowment (waqf), what is its purpose, what is the need for it, and what is the difference between it and ongoing charity (sadaqah jariyah)?

Waqf is the endowment of an asset and the dedication of its usufruct (benefits). It has many benefits, among them is the continuous reward reaching the endower after their death, and the Muslims benefiting from it according to the purpose of the endowment. The need for it increases in our time due to the shortcomings of states in supporting these entities. Waqf is a continuous charity (Sadaqa Jariya).