bonds were put in the game by jagex to battle against the rwt.
you can buy them with real cash and trade them in game to people who don't have real cash but do have 6,7m eoc or 1,3m 07 to buy one. they can redeem it for 14 days per bond but if you have more bonds at the same time u get some extra days. example 1 year mem cost 24 bonds that should be 26 or 27 bonds.