I was wondering what he meant by "indefinite" dysplasia, and when I looked it up I got this:
Indefinite for dysplasia
This is an intermediate reading between negative and low-grade dysplasia. It simply means that the pathologist is not certain whether changes seen in the tissue are due to dysplasia. For example, esophagitis (inflammation of the lining of the esophagus from acid injury) can make cells look atypical so that they resemble dysplastic cells although they are not dysplastic. The pathologist may see other signs of inflammation in the biopsy to help distinguish between inflammatory changes in the tissue and true dysplasia. Sometimes a pathologist may determine that dysplasia is difficult to grade due to inflammation.
It seems maybe you had a lot of inflammation that they thought could be dysplasia but it's not for sure. Did your doc suggest doing another scope with biopsies? I would probably consider that to see if he finds anything this time; chances are it was just inflammation or mild dysplasia that would clear up on its own, but it's better you find out soon just in case. How long ago was this sigmoidoscopy done??