Blade

A blade is any sharpened edge made with the intention of cutting things (but we guess you already knew that).

'Blades' in the SCA

Live Steel

Live steel (any real edged weapon) is strictly forbidden on the field in the the rules of the list. If you are going to be using a knife or similar tool in a way that could hurt anyone you should make sure that no one is nearby and warn anyone who is (this seems obvious but accidents do happen). Some people in the SCA like to say "clear" when they unsheath blades near others.

Heavy fighting

For heavy fighters in the SCA the "blades" on weapons used in combat are in fact strips of electrical tape along the side of the rattan to indicate the cutting edge. The weapon is "blunt" to limit serious damage being inflicted onto fighters (although being hit hard enough with what is essentially a club can hurt anyway).

Fencing

The only group of fighters currently permitted to use a metal blade are fencing combatants. Only blades approved by the fencing marshal are allowed. They must have the prescribed amount of flex, must be unsharpened and must have the tip cut off and replaced by a rubber blunt that is securely held in place.

Re-Enactment Blades

Regular combat blades (called 'live steel' by US re-enactment groups) are basically blunt steel blades. In the UK the standard is to have a 2mm edge, Australia has 1.6mm edge and the majority in the US uses (I believe) 1.6mm. As the edge of the blade is thicker than a historical weapon they tend to be slightly heavier than their historical counterparts. Modern reenactment blade makers are quite good at balancing their weapons for use, but the quality varies.

Semi-sharps are blades that have edges much thinner than regular combat blades and tend to be used in trainbing for western sword arts.

Unfortunately the cost of a weapon does not necessarily indicate its quality. It is a good idea to speak to someone who has purchased a blade from a particular company before purchasing one.