Dirk is a cold piercing weapon, a straight thin dagger with a faceted (mainly rhombic section) double-edged blade.
In the 16th century, a dagger replaced a rapier (a variety of a smallsword). Sailors of the English and Dutch fleets were the first to notice that the dirk was much more convenient than the long piercing weapon due to its short blade. Especially in battles in tight premises, aisles and during boarding. Thus, sailors of the fleets of England and Holland were the first to be armed with dirks.
In everyday life, aristocrats, instead of a long and heavy battle sword, preferred to wear and use a rather short, relatively light, handy and beautiful dirk. It was used to defend on the streets and in travels from robbers, armed mostly with axes and knives.