What is meant by the term "Aqidah" and when did this term appear?

The term "aqeedah" (creed) is not found in the Quran or Sunnah, but its meaning is conveyed by the word "iman" (faith). A Muslim's heart must be firmly bound to the scientific matters that have been authentically reported from Allah and His Messenger, as in the Almighty's saying: "The believers are only those who believe in Allah and His Messenger and then do not doubt" and His saying: "The Messenger has believed in what was revealed to him from his Lord, and [so have] the believers. All of them have believed in Allah and His angels and His books and His messengers." Scholars have unanimously agreed on using this term, and there is no dispute in terminology if the meaning is agreed upon.