After brewing and fermentation there can be unwanted stuff left over in the beer. Things like degenerated yeast cells, haze producing proteins and tannins often remain suspended in the beer. These can all contribute to a hazy or cloudy final product. Clarification agents or finings can be used to fix this problem. They work by chemically bonding with the haze producing elements then precipitating out of the beer by falling to the bottom of the fermentation vessel. The beer is then drained away leaving the unwanted elements behind.
Gelatin and isinglass, made from the air bladders of certain fish, are the most effective finings. Often they remove nearly all of the unwanted elements from beer and are the preferred finings of traditional beer makers like the real ale brewers in the UK who reject filtering.
When combined with filtering, other finings can be quite effective. These include diatomaceous earth and synthetic products like Polycar, nylon and silica gel.