Boyd’s Bible Dictionary:

(heirship). [HEIR.]

Concise Bible Dictionary:

The land of promise is constantly spoken of as the inheritance of Israel: the land flowing with milk and honey was given to them by God (Deut. 4:21; Psa. 105:11, and more). So when Israel returns to take possession of the land in a future day, it is still called their inheritance (Ezek. 45:1, and more). This all shows that they were and will be an earthly people, but God blessed them on earth in relationship with Himself as Jehovah, and will again bless them on earth when they own the Lord Jesus as their Messiah. In connection with this God calls Israel His inheritance: He hath chosen them for His own inheritance (Psa. 33:12; Psa. 78:62, and more).
The Christian has no inheritance on earth; his inheritance is with the saints in light (Col. 1:12): an inheritance incorruptible, and undefiled, and that fadeth not away, reserved in heaven (1 Pet. 1:4). In the meanwhile the Holy Spirit is given as the earnest of the inheritance (Eph. 1:14). It is in Christ Himself the inheritance is obtained, for the Lord Jesus will possess all things in heaven and in earth (Eph. 1:18).

From Anstey’s Doctrinal Definitions:

There are two aspects of the Christian’s inheritance in the New Testament:
•  It is material things—i.e. every created thing in heaven and on earth (Eph. 1:11, 14, 18; Col. 3:24).
•  It is spiritual things that believers possess in Christ—i.e. our spiritual blessings (Acts 20:32; 26:18; Col. 1:12; 1 Peter 1:4).
Viewed as material things, it is called “His (Christ’s) inheritance” (Eph. 1:18) and “our inheritance” (Eph. 1:14) because we are “heirs of God, and joint-heirs with Christ” (Rom. 8:17). Paul said, “All things are yours” (1 Cor. 3:21), and this includes the inheritance. It is something that is ours now (Eph. 1:11 – “we have obtained an inheritance”). It has been purchased for us by Christ’s work on the cross (Heb. 2:9 – “tasted death for every thing”). However, while it belongs to us now, it has yet to be redeemed (Eph. 1:14). The redemption of the inheritance has to do with Christ’s setting it free from sin, Satan, and the world, so that it can be used for the display of His glory in the world to come (the Millennium). This will occur at the Appearing of Christ through His warrior-judgments.
Viewed as spiritual things, the inheritance has to do with what believers possess spiritually in Christ—i.e. our spiritual blessings (Eph. 1:3). Acts 26:18; Colossians 1:12; and 1 Peter 1:4 speak of it in this way. The J. N. Darby Translation renders it “a portion” in Acts 26:18 and Colossians 1:12 to distinguish it from the material side of inheritance. Seen from the perspective of the Christian being on earth, this aspect of the inheritance is viewed as being “in heaven.” J. N. Darby said, “The inheritance is the inheritance of all things that Christ created. But in 1 Peter, or in Colossians 1, the thing is in heaven” (Notes and Jottings, p. 101).

From Manners and Customs of the Bible:

Luke 15:12. The younger of them said to his father, Father, give me the portion of goods that falleth to me. And he divided unto them his living.
Neither Jewish nor Roman law permitted the father to have the arbitrary disposal of all his estate. The property was entailed on the sons at the father’s death, the daughters not being allowed to inherit unless there were no sons. See Genesis 31:14; Numbers 27:8. The general application to this law is seen in the fact that, when Job gave an inheritance to his daughters as well as to his sons, special mention is made of the act as though it were a remarkable occurrence. See Job 42:15. The first-born son received a double share. See Deuteronomy 21:17.
Some commentators, in illustrating this text, suppose that the sons had a right to demand a division of the property during the father’s life-time, and that the father could not refuse such a demand. The text, however, does not necessarily imply this. For all that here appears, it may have been merely a request urged by the son and granted by the father. There is nothing to show that the father was compelled to comply. He did comply, it is true but whether by compulsion or of his own volition is not stated. Mr. Burder (Oriental Customs, 1086) gives an extract from Halbed’s Code of Gentoo Laws, in which it is stated that under certain circumstances the sons had a right to demand of their father a division of his property during his lifetime. There is no evidence, however, that either Jews or Romans had any such law, though they may have been acquainted with it as existing in India.
The verisimilitude of the parable is sufficiently observed, without any reference to a law of compulsion, by supposing it customary sometimes for fathers of their own volition to divide their estate among their sons. This is said to have been sometimes done among the Romans, and that it may have been an occasional custom among the Jews is evident from the example of Abraham, who “gave all that he had” to his son Isaac. See Genesis 24:36; 25:5.