By cup it is meant that from which water is drunk, as is stated in the narrations.
Thaabit radiyallahu anhu relates that Anas radiyallahu anhu showed us a large wooden cup, which was lined with metal, and said, O Thaabit, this is the cup of Rasoolullah sallallahu alaihe wasallam.
It is said that this cup was sold from the estate of Sayyidina Nadr ibn Anas radiyallahu anhu for eight lakh Dirhams and Imaam Bukhari drank water from it in Basrah. Some say that, that was another cup.
Anas radiyallahu anhu says, I gave Rasoolullah sallallahu alaihe wasallam to drink from this cup all those things which are drunk; Nabeedh, milk, etc.
Nabeedh is a drink made by soaking dates, raisins, etc. in water until these things (become soft and) give off its effect. It is a tonic and gives strength. Dates, etc. were soaked for Sayyidina Rasoolullah sallallahu alaihe wasallam at night and he drank it in the morning. It was also sometimes used the next day, provided it did not ferment and become intoxicating.