"Blade" is a generic term used for knives or swords that a combatant might use. In general, firearms are preferred over swords or knives for most combat engagements, but most people still carry a knife for practicality.
In recent times, blades have become a common sight due to the increased usage of magnetic shields. Magnetic shields are personal force fields that users can wear to help deflect bullets. While expensive and not a guarantee, they have been worn by more individuals of higher status, and blades offer flexibility at close distances to circumvent the shields. Thus, blades are part of many special forces and especially amongst the Conduits who might prefer a melee approach.
Blades can be made of a variety of materials, but they are often made to be non-magnetic. The edge of a blade is usually made of the hardest and sharpest material available, and they are incredibly shatter-resistant. Many have a thermal regulator built in to vary their flexibility and hardness.