Halloween or All-Hallows-Eve takes place on the night of 31 October in anticipation of All-Hallows-Day (1st November). It has emerged from a combination of Christian and pagan traditions.
Etymology
Hallow is the old English word for saint.
Halloween is a Scottish variation dating back to the 1700s. The 'een' suffix is a contraction of 'evening'. 'Hallowed evening' or 'holy evening' was later understood to mean eve or 'night before' as with Christmas Eve
All Hallows Day is now called All-Saints-Day in the Catholic calendar. It commemorates Christian martyrs
All Souls Dayfollows on 2 November. On All Souls Day Catholics pray for the 'souls of the (faithful) departed'.