Even if the bride-to-be has been sporting a diamond ring for years, in many Jewish communities, the couple isn't truly engaged until a tena'im (a document detailing the conditions of the engagement) is signed. Breaking an engagement after it's signed is considered extremely dishonorable, so if a tena'im is used, it's almost always signed the day of the wedding [source: Jewish Wedding Network]. This means, of course, that the couple isn't technically engaged until their wedding day.
Tina'ims were first used in medieval times, when Jewish parents would arrange their children's marriages. These documents were contracts and contained the terms agreed upon by the families, including the wedding date, dowry and penalty fee for canceling the union [source: Diamant].