What does Convert, Conversion mean in the Bible?

Dictionary

Baker's Evangelical Dictionary of Biblical Theology - Convert, Conversion
Although the term "conversion" is common in theological and religious discussion today, it was a relatively rare term in the Bible. In its current popular usage it refers to someone who has come to Christ or become a Christian. The biblical roots of the concept involve the use of two terms that mean "to turn" (Heb. sub ; Gk. epistrepho [1]). However, the New Testament usage is more like the common theological meaning. Examples of conversion, outside the New Testament, emerge when one looks at the term "proselyte, " the convert from a Gentile way of life to Judaism. Such an example pictures in everyday Greek terminology what a convert looked like.
The Old Testament . The concept of conversion is actually very rare in the Old Testament. The key term for "turning" is used in a variety of ways that really do not describe conversion. (1) It can refer to nations turning to God in the future (Isaiah 19:22 ). (2) It can describe an Israelite returning to God or, negatively, failing to do so (Isaiah 6:10 ; 31:6 ; Jeremiah 3:10,12 , 14,22 ; Amos 4:6,8 , 10 ; Zechariah 1:2-4 ). A good illustration of this force is Jeremiah 4:1-2 , where the call is to return to God by letting go of idols. (3) Sometimes God is said to return to his people (Isaiah 63:17 ; Amos 9:14 ). In the Old Testament the passage that comes closest to meaning "convert" is Isaiah 55:7 . Here the wicked are called upon to turn to God for mercy and pardon of sin. Those who thirst are to come.
In Judaism . Technical terminology for turning does not occur here, but the example of the proselyte coming to Yahweh from Gentile origins does. Tobit 1:8,13:11 recognize the presence of such proselytes in the synagogue. The term for proselyte is the Hebrew term for "alien" ( ger [2]). Such proselytes would be circumcised, picture their cleansing by engaging in a baptismal washing, offer sacrifices, and would be expected to live a life of moral virtue in contrast to their pagan past. The outstanding picture of such a conversion is the pseudepigraphical story of Joseph and Aseneth.
The New Testament . In the New Testament conversion seems to summarize the call of the church in response to Jesus' commission to preach repentance for the forgiveness of sins to all the nations, as the Old Testament called for (Luke 24:43-47 ). In sum, conversion is a turning to embrace God. So on a few key occasions the concepts of repentance and turning appear together in Acts (3:19; 26:20). Repentance reflects the attitude one brings into conversion, while turning pictures the change of orientation and direction that comes as a part of it (9:35 — turned to the Lord; 11:21 alongside a reference to belief; 14:15 turn from worthless things; 15:19 turn to God; 26:18 turn from darkness to light). This is often Luke's way of describing what Paul refers to as faith, although Paul can speak of "turning to God from idols" as well (1 Thessalonians 1:9-10 ). First Peter 2:25 uses the picture of coming to the great shepherd to express this idea. As one can see, the term can describe what one has turned from or can indicate to whom one turns.
Examples of converts appear throughout the Book of Acts, although the technical terminology is not present. Among such examples are Paul's change of direction at the Damascus road, Cornelius, the instant response of the Philippian jailer, and the picture of Lydia.
Darrell L. Bock
See also Repentance
Vine's Expository Dictionary of NT Words - Convert, Conversion
A — 1: στρέφω (Strong's #4762 — Verb — strepho — stref'-o ) "to turn," is translated "be converted" in Matthew 18:3 , AV. See TURN.
A — 2: ἐπιστρέφω (Strong's #1994 — Verb — epistrepho — ep-ee-stref'-o ) "to turn about, turn towards" (epi, "towards" and No. 1), is used transitively, and so rendered "convert" (of causing a person to turn) in James 5:19,20 . Elsewhere, where the AV translates this verb, either in the Middle Voice and intransitive use, or the Passive, the RV adheres to the Middle Voice significance, and translates by "turn again," Matthew 13:15 ; Mark 4:12 ; Luke 22:32 ; Acts 3:19 ; 28:27 . See COME (again), Note (4), GO (again), RETURN , TURN.
B — 1: ἐπιστροφή (Strong's #1995 — Noun Feminine — epistrophe — ep-is-trof-ay' ) akin to A, No. 2, "a turning about, or round, conversion," is found in Acts 15:3 . The word implies "a turning from and a turning to;" corresponding to these are repentance and faith; cp. "turned to God from idols" (1 Thessalonians 1:9 ). Divine grace is the efficient cause, human agency the responding effect.