From Background to the Daf:

NA'ARAH HA'ME'ORASA

(a) A Na'arah ha'Me'orasa is a girl within six months of reaching physical maturity who has undergone Eirusin (betrothal; see below) but not Nisu'in (marriage; see below.)

1. EIRUSIN - The first stage of Halachic marriage is called Erusin or Kidushin (betrothal). Kidushin can be accomplished in one of three ways:

a) 1. Kesef - A man can be Mekadesh a woman through giving her money or anything equal in value to a Perutah (a very small coin). Upon doing so, he must proclaim, "Harei At Mekudeshes Li b'(-----) Zu" -- "Behold you are betrothed to me through this (-----)".

2. Shtar - A man can be Mekadesh a woman through giving her a marriage document. This may be written upon any surface, and need not be of any specific value. The words "Harei At Mekudeshes Li b'Shtar Zeh" must be written upon the Shtar.

3. Bi'ah - A man can be Mekadesh a woman through having relations with her. At that time, he must proclaim, "Harei At Mekudeshes Li b'Bi'ah Zu". Because Kidushin requires witnesses, the Chachamim strongly condemned anyone who uses this method of Kidushin.

b) The Torah refers to this stage of marriage as "Eirusin" (Devarim 22:23). The term "Kidushin" is used by the Rabanan in order to connote that just as everyone is prohibited to benefit from Hekdesh (an object sanctified to the service of Hash-m), through Kidushin a woman becomes prohibited to everyone in the world save her husband (Kidushin 2b; see also Tosfos 7a DH v'Nifshetu).

c) At the time that Kidushin takes place a Berachah known as Birkas Eirusin is recited (Kesuvos 7b).

2. NISU'IN - the completion of the marriage, accomplished through Chupah (see Background to Kesuvos 57:1). Nisu'in requires that the husband give his wife a Kesubah. Following this stage the husband brings his wife into his house, and they live as man and wife.

I hope that you found this information helpful!

Moshe Binyamin Cohen