Clostridioides difficile (also known as C.difficile or C.diff) is a type of bacteria which can be found in the large bowel which can cause diarrhoea and most commonly affects people who have recently been treated with antibiotics. C.diff infections can be unpleasant and can sometimes cause serious bowel problems, but can usually be treated with another course of antibiotics. Further information can be found here:
https://www.nhs.uk/conditions/c-difficile/