What is Sadaqa?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Sadaqa or giving alms means: "Giving something to somebody without seeking a substitute in return and with the intention to please Allah".
Sadaqa usually refers to voluntary alms in particular. al-Khatib al-Shirbeeni says: 'Voluntary alms is what is meant when Sadaqa is mentioned out of a particular context'.
al-Ragib al-Asfahani says: 'Sadaqa is what the person gives from what he possesses like Zakah hoping to get nearer to Allah. But initially Sadaqa is what is given voluntarily while Zakah is what is given obligatorily'. But Sadaqa can also be said to express Zakah. Allah Says (interpretation of meaning): {As-Sadaqat (here it means Zakat) are only for the Fuqara' (poor), and Al-Masakin (the poor) …} [9: 60]. Allah also Says (interpretation of meaning): {Take Sadaqah (alms) from their wealth in order to purify them and sanctify them with it, …} [9: 103].
Sadaqa can also be used to express the Waqf (endowment) as in the Hadith reported by al-Bukhari that the Prophet said, "If you like you can give the land as endowment and give its fruits in charity". So Umar gave it in charity as an endowment on the condition that would not be sold nor given to anybody as a present and not to be inherited" ,
It is also used to express any type of expenditures. The Prophet (Sallallahu Alaihi wa Sallam) said: "Every good deed is a charity" . [Reported by Imam al-Bukhari ].
Allah knows best.