Bad Biology is exactly what you would think it is: improper portrayal of organisms. Bad biology may take the form of anatomy, physiology, genetics, diseases, and more. While biology is a topic that is taught in most schools, for some reason it escapes many writers... and even if one did not study biology in school, ignorance is not an excuse when resources are as simple as a click away on the internet. In this respect, it's similar to Bad Psychology. Bad biology is a large contributor to squick.