What wager is involved in the final part of Taming of the Shrew?

At the end of Taming of the Shrew, Katharine and Petruchio visit Baptista, where two other newly wedded couples are present: Bianca and Lucentio and Hortensio and his bride. Petruchio wins a wager about which of the wives is the most obedient and submissive. Katharine is famous from that day forth as the most obedient and duteous wife in Padua.