Mrrzy - conkers are the seed of the Horse-Chestnut tree. They're a nut about 1" in diameter (and look rather like sweet-chestnuts as someone else has already said). They're drilled thought by kids here and a piece of string threaded through, then they take it in turns to swing their conker at their opponent's conker in an effort to smash it. The unsmashed conker is the 'champion'. They're named for the number of contests they've won - e.g. a 'two-er' or a 'three-er' etc.