The literal meaning of the Arabic term ‘Shaytaan’ is one who transgresses the boundaries of Allah, or is a consistent disobedient or denier of the Truth.
The leader of all the ‘Shaytaans’ is the accursed evil one who is named ‘Iblees’, the literal meaning of which means one who constantly doubts and despairs.
Allah says in the Holy Quran Chapter 18 Surah Kahf verse 50:
Behold! We said to the Angels “Bow down to Adam”: they bowed down except Iblis. He was one of the Jinns, and he broke the Command of his Lord. Will ye then take him and his progeny as protectors rather than Me? And they are enemies to you! Evil would be the exchange for the wrongdoers!
Iblees is the name of one amongst the Shayateen, and is mentioned in the Glorious Quran by name in the episode of the creation of Hadrat Adam (a.s.). All those amongst the Jinns and the human beings who follow the mission of disobedience of ‘Iblees’ are all termed ‘Shaytaans’ by Allah Subhanah.
Allah says in the Holy Quran Chapter 6 Surah Anaam verse 112:
And so have We (Allah) always set against every Prophet enemies from among Shaitaans of men and Shaitaans of jinns, who inspire one another with flowery discourses by way of deception.
Whenever Allah Subhanah refers to ‘As-Shaytaan’ (The Shaytaan) it refers to the accursed leader of the Shayateen, Iblees; and whenever the general term ‘shaytaan’ or plural ‘shayateen’ is used, it refers to all those amongst the men and the jinn who follow the mission of disobedience of the accursed Iblees.
Allah Says in the Holy Quran Chapter 4 Surah Nisaa verses 120-121:
Satan promises them and arouses desire in them. But Satan does not promise them except delusion.An-Nisaa (4:120)
The refuge of those will be Hell, and they will not find from it an escape.An-Nisaa (4:121)
Allah Says in the Holy Quran Chapter 6 Surah Anaam verse 43: When the suffering reached them from Us why then did they not learn humility? On the contrary their hearts became hardened, and Shaytaan made their (sinful) acts seem fair-seeming to them.
Allah Says in the Holy Quran Chapter 14 Surah Ibraheem verse 22: And Shaytaan will say when the matter is decided (on the Day of Judgment): “It was Allah Who gave you a promise of Truth: I too promised but I failed in my promise to you. I had no authority over you except to call you but ye listened to me: then reproach not me but reproach your own souls. I cannot listen to your cries nor can ye listen to mine. I reject your former act in associating me with Allah. For wrongdoers there must be a Grievous Penalty.”