The term crusade used in modern historiography at first referred to the wars in the Holy Land beginning in 1095, but the range of events to which the term has been applied has been greatly extended, so that its use can create a misleading impression of coherence, particularly regarding the early Crusades. The term used for the campaign of the First Crusade was iter "journey" or peregrinatio "pilgrimage". The terminology of crusading remained largely indistinguishable from that of pilgrimage during the 12th century, reflecting the reality of the first century of crusading where not all armed pilgrims fought, and not all who fought had taken the cross. It was not until the late 12th to early 13th centuries that a more specific "language of crusading" emerged. Pope Innocent III used the term negotium crucis "affair of the cross" for the Eastern Mediterranean crusade, but was reluctant to apply crusading terminology to the Albigensian crusade. The Song of the Albigensian Crusade from about 1213 contains the first recorded vernacular use of the Occitan crozada. This term was later adopted into French as croisade and in English as crusade. The modern spelling crusade dates to c. 1760. Sinibaldo Fieschi (the future pope Innocent IV) used the terms crux transmarina for crusades in Outremer against Muslims and crux cismarina for crusades in Europe against other enemies of the church.
The Crusades in the Holy Land are traditionally counted as nine distinct campaigns, numbered from the First Crusade of 1095–99 to the Ninth Crusade of 1271–72. This convention is used by Charles Mills in his History of the Crusades for the Recovery and Possession of the Holy Land (1820) and is often retained for convenience even though it is somewhat arbitrary. The Fifth and Sixth Crusades led by II may be considered a single campaign, as can the Eighth Crusade and Ninth Crusade led by IX.
In modern historiography, the term "Crusade" may differ in usage depending on the author. Giles Constable describes four different perspectives among scholars:
- Traditionalists restrict their definition of the Crusades to the Christian campaigns in the Holy Land, "either to assist the Christians there or to liberate Jerusalem and the Holy Sepulcher", during 1095–1291.
- Pluralists use the term Crusade of any campaign explicitly sanctioned by the reigning Pope. This reflects the view of the Roman Catholic Church (including medieval contemporaries such as Saint Bernard of Clairvaux) that every military campaign given Papal sanction is equally valid as a Crusade, regardless of its cause, justification, or geographic location. This broad definition includes attacks on paganism and heresy such as the Albigensian Crusade, the Northern Crusades, and the Hussite Wars, and wars for political or territorial advantage such as the Aragonese Crusade in Sicily, a Crusade declared by III against Markward of Anweiler in 1202, one against the Stedingers, several (declared by different popes) against Emperor II and his sons, two Crusades against opponents of King Henry III of England, and the Christian re-conquest of Iberia.
- Generalists see Crusades as any and all holy wars connected with the Latin Church and fought in defence of the faith.
- Popularists limit the Crusades to only those that were characterised by popular groundswells of religious fervour – that is, only the First Crusade and perhaps the People's Crusade.
The Arabic loanword Muslim is first attested in English in the 17th century. Before this the common term for Muslim was Saracen, in origin referring to the pre-Islamic, non-Arab inhabitants of the desert areas around the Roman province of Arabia. The term evolved to include Arab tribes, and by the 12th century it was an ethnic and religious marker in Medieval Latin literature corresponding to modern "Muslim".
Frank and Latin were used during the Crusades for Western Europeans, distinguishing them from Greeks. Medieval Muslim historiographers such as Ali ibn al-Athir refer to the Crusades as the "Frankish Wars" (ḥurūb al-faranǧa حروب الفرنجة).
The term used in modern Arabic, ḥamalāt ṣalībiyya حملات صليبية, lit. "campaigns of the cross", is a loan translation of the term Crusade as used in Western historiography.