What is an Empty Leg ?

As the term suggests, empty legs are flights that are scheduled to fly without any passengers. These operate when an aircraft needs to reposition or return for a charter. 

They are sometimes also referred to as dead-heads, repositioning legs, and ferry flights. According to charter-jet companies, 30%-50% of the private jet charter fleet often flies empty. 

Given how costly they are to operate, charter companies try to avoid having to fly empty legs in the first place. As a result, they are often not made available until fairly last minute.