PRF codes are standardized across military alliances to allow for seamless interoperability between different branches of service and coalition partners. In NATO forces, for instance, PRF coding is governed by standardization agreements (such as STANAG 3733) and typically utilizes a three- or four-digit numerical code.
In the world of Fire Emblem Heroes (and the mainline series), not all swords are created equal. You can inherit a Slaying Edge+ or a Deck Swabber+ onto almost anyone, but there is a special class of weapon that separates the lords from the levees, the gods from the grunts: the (short for "Preferred" or "Personal" weapon). prf weapon