A cannula is a tube that can be inserted into the body, often for the delivery or removal of fluid or for the gathering of samples. In simple terms, a cannula can surround the inner or outer surfaces of a trocar needle thus extending the effective needle length by at least half the length of the original needle. Its size mainly ranges from 14 to 26 gauge. Different-sized cannula have different colours as coded.

A trocar is a medical or veterinary device used in minimally invasive surgery. Trocars are typically made up of an awl, a cannula and often a seal. Some trocars also include a valve mechanism to allow for insufflation. Trocars are designed for placement through the chest and abdominal walls during thoracoscopic and laparoscopic surgery, and each trocar functions as a portal for the subsequent insertion of other endoscopic instruments such as grasper, scissors, stapler, electrocautery, suction tip, etc. — hence the more commonly used colloquial jargon "port". Trocars also allow passive evacuation of excess gas or fluid from organs within the body.