Ice Beer.

In recent years, thanks to the mainstream brewers, ice beer has gotten a bad rap.
Traditionally it was simply a lagered beer which was stored at temperatures slightly below freezing.
While in this state ice crystals can be filtered out to give a much higher alcohol content and this is particularly true of Eisbock beers.
When beer is left to age like this for long periods of time (3 months or usually more) the tastes can mellow nicely and produce very smooth beer (both ales and lagers) with crisp clean finishes.
Various initial styles of beer can be treated this way and each will produce a different final profile all seeming to have a sharp crisp clean finish.
Main stream producers don't use the process to age their beer, many of them simply use it to jack up the alcohol content and make pretty advertising pictures.