A dagger is a fighting knife
Fighting knife
A fighting knife is a knife with a blade designed to inflict a lethal injury in a physical confrontation between two or more individuals at very short range...

 with a sharp point designed or capable of being used as a thrusting or stabbing weapon. The design dates to human prehistory, and daggers have been used throughout human experience to the modern day in close combat
Close combat
*Close combat is a generic term for both Close Quarters Battle and Hand to hand combat.*Mêlée generally refers to disorganized close combat.*CQB is an acronym for Close Quarters Battle, such as that which occurs in urban warfare....

 confrontations. Many ancient cultures used adorned daggers in ritual and ceremonial purposes, a trend which continues to the present time in the form of art knives. The distinctive shape and historic usage of the dagger have made it iconic and symbolic.

Over the years, the term 'dagger' has been used to describe a wide variety of thrusting knives, including knives that feature only a single cutting edge, such as the European rondel dagger or the Persian pesh-kabz
Pesh-kabz, Pesh-quabz, Pesh-kabj, or Pish-ghabz is the name of an Indo-Persian-Afghan knife used in Safavid Persia, Mughal India, and some nations of central Asia...

, or, in some instances, no cutting edge at all, such as the stiletto
A stiletto is a knife or dagger with a long slender blade and needle-like point, intended primarily as a stabbing weapon. The stiletto blade's narrow cross-section and acuminated tip reduces friction upon entry, allowing the blade to penetrate deeply...

 of the Renaissance.