'firstfruits' definitions:

Definition of 'firstfruits'

First-fruits The first-fruits of the ground were offered unto God just as the first-born of man and animals.
The law required,
That on the morrow after the Passover Sabbath a sheaf of new corn should be waved by the priest before the altar (Lev. 23:5, 6, 10, 12; 2:12).
That at the feast of Pentecost two loaves of leavened bread, made from the new flour, were to be waved in like manner (Lev. 23:15, 17; Num. 28:26).
The feast of Tabernacles was an acknowledgement that the fruits of the harvest were from the Lord (Ex. 23:16; 34:22).
Every individual, besides, was required to consecrate to God a portion of the first-fruits of the land (Ex. 22:29; 23:19; 34:26; Num. 15:20, 21).
The law enjoined that no fruit was to be gathered from newly-planted fruit-trees for the first three years, and that the first-fruits of the fourth year were to be consecrated to the Lord (Lev. 19:23-25). Jeremiah (2:3) alludes to the ordinance of "first-fruits," and hence he must have been acquainted with the books of Exodus, Leviticus, and Numbers, where the laws regarding it are recorded.