At the end of the boil, solid particles in the hopped wort are separated out, usually in a vessel called a whirlpool or settling tank.Whirlpool systems vary smaller breweries tend to use the brew kettle, larger breweries use a separate tank, and design will differ, with tank floors either flat, sloped, conical or with a cup in the centre. 

The principle in all is that by swirling the wort the centripetal force will push the trub into a cone at the centre of the bottom of the tank, where it can be easily removed.