Also known as hand and a half swords, they appeared in virtually all West European countries after 1000 AD and remained in use well into the 1500s.
They featured a long, straight blade (approx. 70-100 centimetres) and a slightly longer than usual hilt (sometimes up to 20-25 cm). They were neither a smaller single-handed sword, nor the massive two-handed type. Rather, they were a "bastard" version of both.
The name "bastard sword" could also refer to any bladed tool sharpened on only one edge (eg. a bastard-saw or bastard-file).