Moors
"Moors" originates from the Latin "maurus" - "dark" or metaphorically "dark-skinned" and was originally the established term used in Roman Italy and Spain for the inhabitants of Northern Africa. In the late Middle Ages "Moors" became a synonym for "Muslims" and a fixed constituent of the Christian polemic against Islam. This polemic that wanted to portray Islam as Christian heresy instead of an independent religion was based on the following story: In the days of the apostles a Roman deacon, an evil and dishonorable man named Nikolaus, sought to become the pope; the vileness he did to do this brought about his excommunication and imprisonment until his death. His most devoted apprentice, Maurus, left the city disguised as a Monk and fled to Arabia. The people there admired him as a religious recluse. In order to avenge his Master Nikolaus he took a camel herder, called Mohammed as an apprentice and taught him the satanic arts and had him appointed as king under mysterious circumstances. Together they authored a thick book (the Koran), with content based off of the Old and New Testaments but which changed them in the most scandalous way in order to ruin Christianity. "Moors" are then related in this sense that they are the followers of Maurus.

Mohammedans
"Mohammedan" is an antiquated term for "Muslims" that was disclaimed by the Muslims themselves, as the prophet Mohammed does not receive godlike reverence in Islam. It originates from the time when Christians considered Islam heresy instead of its own religion. From the Christian perspective the term "Mohammedan" was given to those who followed the "false prophet" Mohammed.

Muslims
"Muslims" are the followers of Islam. "Muslim" literally means "one who comes from God." Muslims are all those who acknowledge one God, his word (Torah, Psalter, the gospels, Koran), his prophets, his angels and the Last Judgment.

Saracen
In the later Greek and roman antiquity Saracen (Greek "Sarkenos") meant simply "Arabs"; though the linguistic origin of the word is still unknown. With the spread of Islam, "Saracen" was used as a synonym for "Muslim." Since the time of the Crusades, European literature used the term "Saracen" to describe the antagonistic Muslims of Syria, Palestine, Egypt, and Spain. The meaning of "Arabs" was then increasingly left in history.

Seldjukian
The "Seljukian," originated in Central Asia as one of the Turkish sovereign dynasties that is named after its forefather "Seljuk." In the second half of the 11th century, the Seljukians were able to bring Asia and Asia Minor under their control. After they had conquered the regions of present-day parts of Southwest Azerbaijan, Iran, and Iraq, they hit the united Byzantine army near Manzikert (Malazgirt) in 1071 and conquered nearly all of Anatolia as well as parts of Syria and Palestine in the time that followed. The call for help from the Byzantine Emperor to Rome that caused the Crusades was not for the deliverance of Jerusalem, but for a general support in the fight against the Seldjukians. At the beginning of the first Crusade (1095-99) the Sunni Seldjukians were the most powerful political opponents of the Shiite Fatimid Caliphate residing in Cairo. From 1071-1098 they also controlled Jerusalem before it fell to Fatimite rule shortly before its capture due to the crusaders (1071-1098).