The thick lower end of the digestive tract where solid waste is gathered and leaves the body is called the rectum.

Here's a breakdown:

* Large Intestine: The final part of the digestive system, responsible for absorbing water and forming stool.

* Rectum: The last section of the large intestine, where stool is stored before elimination.

* Anus: The opening at the end of the rectum through which stool is expelled.

So, the rectum is where the waste is stored and the anus is where it exits the body.