There is an exchange in this book wherein Tam asks Carter if he thinks the Stanley Cup is the Holy Grail, and Carter looks at him like he's stupid and says it doesn't have to be, it's the Stanley Cup. So that's the emotional meaning of it.

Literally it is the best trophy in all of sports, a great huge silver thing that's had silver rings engraved with team name and year added to it since 1892. There is not a prize in North American sports older, and certainly none more venerable.