HOLY WEEK (t^o/idj yueyaXrj, ayla or rCiv ayiwv, eurpaKTOs, also ityiepai. iraSTj/uaTtoc, i7yuepai oraijpcbcujuai: hebdomas [or seplimana] major, sancta, authenlica [i.e. canonizata, du Cange], ultima, poenosa, luctuosa, nigra, inofficiosa, muta, crucis, lamentationum, indulgent iae) , in the Christian ecclesiastical year the week immediately preceding Easter. The earliest allusion to the custom of marking this week as a whole with special observances is to be found in the Apostolical Constitutions (v. 18, 19), dating from the latter half of the 3rd century A.D. Abstinence from wine and flesh is there commanded for all the days, while for the Friday and Saturday an absolute fast is enjoined. Dionysius Alexandrinus also, in his canonical epistle (260 A.D.), refers to the six fasting days (e T&V vqartiSiv rifjJtpaC) in a manner which implies that the observance of them had already become an established usage in his time. There is some doubt about the genuineness of an ordinance attributed to Constantine, in which abstinence from public business was enforced for the seven days immediately preceding Easter Sunday, and also for the seven which followed it; the Codex Theodosianus, however, is explicit in ordering that all actions at law should cease, and the doors of all courts of law be closed during those fifteen days (1. ii. tit. viii.). Of the particular days of the " great week " the earliest to emerge into special prominence 'was naturally Good Friday. Next came the Sabbatum Magnum (Holy Saturday or Easter Eve) with its vigil, which in the early church was associated with an expectation that the second advent would occur on an Easter Sunday.
For details of the ceremonial observed in the Roman Catholic Church during this week, reference must be made to the Missal and Breviary. In the Eastern Church the week is marked by similar practices, but with less elaboration and differentiation of rite. See also EASTER, GOOD FRIDAY, MAUNDY THURSDAY, PALM SUNDAY and PASSION WEEK.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)