Silent distilleries are distilleries that are no longer in operation. Some have just been mothballed for a while (usually due to financial constraints or because of a new site opening elsewhere that relocated the bulk of production) while others may have been abandoned and demolished completely.
The bottlings and casks from these distilleries can gain cult status, especially on the secondary market with many of the auction houses’ big-ticket items coming from there. Some famous Scotch names include Port Ellen, Rosebank, Coleburn while Karuizawa Japanese Whisky (closed since 2001) enjoys near mythic status.