First-fruits (Greek, ἀπαρχὴ, aparche) were the first portions of produce, animals, and/or family that were given to the Lord. The firstborn child:

Numbers 18:14-17, “Every devoted thing in Israel shall be yours. 5 “Every first issue of the womb of all flesh, whether man or animal, which they offer to the Lord, shall be yours; nevertheless the firstborn of man you shall surely redeem, and the firstborn of unclean animals you shall redeem. 16 “As to their redemption price, from a month old you shall redeem them, by your valuation, five shekels in silver, according to the shekel of the sanctuary, which is twenty gerahs. 17 “But the firstborn of an ox or the firstborn of a sheep or the firstborn of a goat, you shall not redeem; they are holy. You shall sprinkle their blood on the altar and shall offer up their fat in smoke as an offering by fire, for a soothing aroma to the Lord.”

Jesus is said to be the first-fruits of the resurrection:

“Christ has been raised from the dead, the first fruits of those who are asleep, for since by a man came death, by a man also came the resurrection of the dead. 22  For as in Adam all die, so also in Christ all will be made alive. 23 But each in his own order: Christ the first fruits, after that those who are Christ’s at His coming,” (1 Cor. 15:20-23).

The first believers in an area are also said to be first-fruits:

• Romans 16:5, “Also, greet for me the church that meets at their house. Greetings to my dear friend Epenetus, who was the first (aparche) person in Asia to follow Christ.”
• 1 Cor. 16:15, “You know that the family of Stephanas were the first believers in Southern Greece and that they have given themselves to the service of God’s people. I ask you, brothers and sisters,”