Boyd’s Bible Dictionary:

(in promise). To pledge troth, that is, engage to marry. A betrothed woman was regarded as the lawful wife of her spouse, and he could not break off the match without a divorce, while she, if unfaithful, would be considered an adulteress.

Concise Bible Dictionary:

Among the Jews this was looked upon as being as binding as marriage, and could not be dissolved except by divorce. Certain laws were given as to a betrothed woman (Ex. 21:8-9; Deut. 20:7; Deut. 28:30). Mary, the mother of the Lord Jesus, was betrothed to Joseph, and he contemplated putting her away privately, but was instructed as to the truth of her condition by the angel of the Lord (Matt. 1:18-19; Luke 1:27; Luke 2:5). It is used symbolically to express Jehovah’s favor to His ancient people in a future day, when He will “betroth” them to Himself forever (Hos. 2:19-20). Also as to the position in which the church stands to Christ: Paul wrote to the Corinthian saints “I have espoused you to one husband, that I may present you as a chaste virgin to Christ” (2 Cor. 2:2). The conduct of the saints should be true to this betrothal.

From Manners and Customs of the Bible:

Judges 14:7-8. He went down, and talked with the woman; and she pleased Samson well. And after a time he returned to take her.
The former part of this passage has reference, doubtless, to the betrothal; the latter part, to the marriage. About a year usually elapsed between betrothal and marriage, though this was not always the case. The expression “after a time,” literally, after days, is sometimes equivalent to a year.
See also note on Matthew 1:18 (#629).