What is the meaning of the word 'Aqidah (creed/doctrine)?

Praise be to Allah.

A creed is the matters to which souls give belief and hearts confidently adhere. It is derived from the word ( aqd) which indicates necessity and assurance. In Sharia, creed refers to scientific matters that a Muslim must hold in his heart and believe in with firm faith without doubt, because Allah has mentioned them in His Book or through His revelation to His Messenger. The principles of creeds include belief in Allah, His angels, His books, His messengers, and the Last Day, as stated in the Quran and Gabriel's Hadith. Thus, creed in Islam is the established scientific matters about Allah and His Messenger which a Muslim must believe in with conviction.