The term die-cast toy here refers to any toy or collectible model produced by using the die casting method. The toys are made of metal and plastic, the metal used commonly is zamak (or Mazak), an alloy of zinc and aluminium. Zamak is also referred to as white metal or pot metal. The most common die-cast toys are scale models of automobiles, aircraft, construction equipment and trains, although almost anything can be produced by this method.

The obove statement is from http://en.wikipedia.org/wiki/Die-cast_toy and contains the most basic information. For more history, you can view that article.