Boyd’s Bible Dictionary:

(free burning). The yellowish gum used in sacrificial fumigation (Ex. 30:7-97And Aaron shall burn thereon sweet incense every morning: when he dresseth the lamps, he shall burn incense upon it. 8And when Aaron lighteth the lamps at even, he shall burn incense upon it, a perpetual incense before the Lord throughout your generations. 9Ye shall offer no strange incense thereon, nor burnt sacrifice, nor meat offering; neither shall ye pour drink offering thereon. (Exodus 30:7‑9); Lev. 16:12,1312And he shall take a censer full of burning coals of fire from off the altar before the Lord, and his hands full of sweet incense beaten small, and bring it within the vail: 13And he shall put the incense upon the fire before the Lord, that the cloud of the incense may cover the mercy seat that is upon the testimony, that he die not: (Leviticus 16:12‑13); Rev. 8:33And another angel came and stood at the altar, having a golden censer; and there was given unto him much incense, that he should offer it with the prayers of all saints upon the golden altar which was before the throne. (Revelation 8:3)). A mixture of gums and spices (Ex. 30:34-3834And the Lord said unto Moses, Take unto thee sweet spices, stacte, and onycha, and galbanum; these sweet spices with pure frankincense: of each shall there be a like weight: 35And thou shalt make it a perfume, a confection after the art of the apothecary, tempered together, pure and holy: 36And thou shalt beat some of it very small, and put of it before the testimony in the tabernacle of the congregation, where I will meet with thee: it shall be unto you most holy. 37And as for the perfume which thou shalt make, ye shall not make to yourselves according to the composition thereof: it shall be unto thee holy for the Lord. 38Whosoever shall make like unto that, to smell thereto, shall even be cut off from his people. (Exodus 30:34‑38)).

Concise Bible Dictionary:

Frankincense—Boswellia Sacra
A fragrant resin. It was an ingredient in the holy anointing oil, and was used in the temple service (Ex. 30:3434And the Lord said unto Moses, Take unto thee sweet spices, stacte, and onycha, and galbanum; these sweet spices with pure frankincense: of each shall there be a like weight: (Exodus 30:34); Lev. 2:1, 15-161And when any will offer a meat offering unto the Lord, his offering shall be of fine flour; and he shall pour oil upon it, and put frankincense thereon: (Leviticus 2:1)
15And thou shalt put oil upon it, and lay frankincense thereon: it is a meat offering. 16And the priest shall burn the memorial of it, part of the beaten corn thereof, and part of the oil thereof, with all the frankincense thereof: it is an offering made by fire unto the Lord. (Leviticus 2:15‑16)
; Lev. 5:1111But if he be not able to bring two turtledoves, or two young pigeons, then he that sinned shall bring for his offering the tenth part of an ephah of fine flour for a sin offering; he shall put no oil upon it, neither shall he put any frankincense thereon: for it is a sin offering. (Leviticus 5:11); Lev. 24:77And thou shalt put pure frankincense upon each row, that it may be on the bread for a memorial, even an offering made by fire unto the Lord. (Leviticus 24:7); Song of Sol. 3: 6, Song of Sol. 4: 6, 14). It formed part of the gifts presented to the Lord by the Magi (Matt. 2:1111And when they were come into the house, they saw the young child with Mary his mother, and fell down, and worshipped him: and when they had opened their treasures, they presented unto him gifts; gold, and frankincense, and myrrh. (Matthew 2:11)); and was among the things carried to Babylon the Great (Rev. 18:1313And cinnamon, and odors, and ointments, and frankincense, and wine, and oil, and fine flour, and wheat, and beasts, and sheep, and horses, and chariots, and slaves, and souls of men. (Revelation 18:13)). It is traced to the Boswellia serrata of the botanists, which grows in India. By cutting slits in the bark the gum exudes. The best is white and bitter to the taste, though the yellowish in color is extensively used. The Mahometans choose the white, but the Greek and Roman churches use much of the colored.
Frankincense—Boswellia Serrata