Historical fencing refers to any type of self-defense martial arts from pre-modern times, typically referring to European-centric fighting techniques, both armed and unarmed. It’s a very broad term that encompasses that type of fencing practice and study found in Historical European Martial Arts (HEMA) and the Society for Creative Anachronism (SCA). It is sometimes synonymous to the term western martial arts (WMA).
It differs from modern sport fencing you’d see in the Olympics in the weapons used, the protective clothing worn, rule sets, and tournament space, among other things.