A trocar is a pen-shaped instrument with a sharp triangular point at one end. It is used inside a hollow tube, known as a cannula or sleeve, to create an opening into the body. The trocar allows placement of other laparoscopic instruments, such as graspers, scissors, and staplers. 

Trocars are used in laparoscopic procedures and other minimally invasive surgery (MIS) to make small, puncture-like incisions in outer tissue layers. These incisions allow surgeons to insert cannulas through which surgical instruments can be introduced.