Mystery Theme III by KlionskyG

Question 12

What is the theme of this quiz?

OMER - Every answer contains these four letters consecutively. The Omer is the 7 week period between the Jewish holidays of Passover and Shavuot, the aforementioned period of the barley harvest, which is counted day by day: "today is x days of the Omer, which are w weeks and d days of the Omer"