Fecal microbiota transplant (FMT), also known as a stool transplant, is exactly what it sounds like. It involves taking the feces from a healthy donor (with no known diseases) and putting it into someone who is sick.
There are a number of ways this transfer can happen: via a slurry delivered down through a nasal to gastric tube, or from the bottom up by an enema or a colonoscopy, or orally in the form of a capsule filled with freeze dried material.
These procedures are designed to help restore the microbe balance in the gut. They have been shown to be effective for treating some gastrointestinal conditions (inflammatory bowel diseases) but there is also a lot of research being conducted for experimental treatments across a wide range of health issues that have been linked to the human microbiome including obesity and autism.
However, a death in 2019 lead to an FDA warning about proper testing of the material used for FMT and the procedure is not without unpleasant side effects. It is very important to understand that feces can contain dangerous microbes and that a fecal transplant should NEVER be done without proper medical supervision.
Photo credit: Let Them Eat Dirt documentary