The counting of the days from Passover until Shavuot, called Counting of the Omer (Sfirat Haomer), based on the agricultural backdrop of the harvest days: “Speak to the Israelites and say to them: ‘When you enter the land I am going to give you and you reap its harvest, bring to the priest a sheaf of the first grain you harvest.” (Leviticus 23:10)

In the Bible, the symbol of the harvest festival was “two loaves”:

From wherever you live, bring two loaves made of two-tenths of an ephah of the finest flour, baked with yeast,   as a wave offering of first fruits to the Lord.  (Leviticus 23:17)
 

The harvest festival also provides the backdrop of social precepts such as giving charity to the needy:

“When you reap the harvest of your land, do not reap to the very edges of your field or gather the gleanings of your harvest. Leave them for the poor and for the foreigner residing among you. I am the Lord your God.” (Leviticus 23:22)

The Omer is an amount of grain harvested. The beginning of the Omer was brought in an elaborate ceremony to the Temple on the second day of Passover. After the ceremony, it was permitted to eat from the year’s new grain.
Peah - the edges of the field, left for the needy.
Leket - sheaves that fall while performing the harvest. These, together with the Shikhah (“forgetfulness”) left in the field, the Torah instructs us to leave to the poor, the foreigner, the orphan and the widow.