Well, "vis" is an adjective and means wise and "vise" in "de vise" is what we call "ett substantiverat adjective" (an adjective used a s a noun). Sorry, but I don't know the English word for that :).
Other examples are "den gamle är trött" (the old man is tired) and "de unga skrattar högt" (the young ones lol).
Next question is, I suppose, why it is "de vise" and not "de visa". I guess that the e ending is an old plural form that has been kept in some fixed expressions like "de vises sten" och "de tre vise männen". There is also "di blåe" (de blå), which is a popular name of MFF, the Malmö football club.
PS. Oops, I just realized that this is from the Norwegian course and not from the Swedish course. So let's just hope that the same rules hold ha ha.
Thanks - this is a great explanation. I don't think there is a name for ett substantiverat adjective in English - just adjective used as a noun.
The only problem is that I am Swedish and don't have a clue what I am talking about when it comes to Norwegian :).