"And you shall bring an omer of the first cuttings of your harvest"Leviticus 23:10.

On the sixteenth day of Nissan [the second day of Passover], we are commanded to bring a barley offering in the Holy Temple, accompanied by a lamb (in its first year of life). This offering is known as the Minchat Bikurim [more popularly identified as the Omer Offering].