Most Christians refer to the week before Easter as "Holy Week"—it contains the days of the Easter Triduum, including Maundy Thursday, commemorating the Maundy and Last Supper, In Western Christianity, Eastertide, or the Easter Season, begins on Easter Sunday and lasts seven weeks, ending with the coming of the fiftieth day, Pentecost Sunday.
In Eastern Christianity, the season of Pascha begins on Pascha and ends with the coming of the fortieth day, the Feast of the Ascension.
Easter therefore varies between 4 April and 8 May on the Gregorian calendar (the Julian calendar is no longer used as the civil calendar of the countries where Eastern Christian traditions predominate).
Also, because the Julian "full moon" is always several days after the astronomical full moon, the eastern Easter is often later, relative to the visible moon's phases, than western Easter.
While martyrs' days (usually the individual dates of martyrdom) were celebrated on fixed dates in the local solar calendar, the date of Easter was fixed by means of the local Jewish lunisolar calendar.