Boyd’s Bible Dictionary:

Were offerings and priest’s perquisites
(Ex. 22:29; 23:19; 34:26; Lev. 2:12; 23:10-12; Num. 18:12; Deut. 18:3-4).

Concise Bible Dictionary:

1. As God had claimed the first-born of man and beast, so also he claimed the first of the first-fruits, that they might be presented as an acknowledgment that God was the giver of them, and thanks be rendered for His gifts. All the males were to present themselves three times in the year before God, and these occasions were arranged at the times of ingathering of the barley (at the Feast of Unleavened Bread); of wheat (at the Feast of Weeks); and of the vintage (at the Feast of Tabernacles) (Ex. 23:16, 19; Ex. 34:22, 26; Deut. 18:4; Deut. 26:10; Ezek. 48:14).
2. Christians are said to have the first-fruits of the Spirit: they have the earnest or pledge of still future and larger blessing (Rom. 8:23; 2 Cor. 5:5; Eph. 1:14).
3. Those first gathered to God in any economy are called the first-fruits (Rom. 11:16; Rom. 16:5; 1 Cor. 16:15; Jas. 1:18; Rev. 14:4).
4. Christ, being raised from among the dead, is the first-fruits of them that sleep (1 Cor. 15:20, 23). “First-fruits” necessarily imply that there are more like them to follow.