“The omer refers to the 49-day period between the second night of Passover (Pesach) and the holiday of Shavuot. This period marks the beginning of the barley harvest when, in ancient times, Jews would bring the first sheaves to the Temple as a means of thanking God for the harvest. The word omer literally means “sheaf” and refers to these early offerings.”
As Catholics we count the days from Easter to the Ascension, and then the days to Pentecost. Actually, Jews reckon Shavuot as Pentecost, celebrating the giving of the Torah, as a special holy day in itself.