Google says: A hole in a mathematical object is a topological structure which prevents the object from being continuously shrunk to a point

Which is as clear as dirt. My understanding of it is to take every point on an object and make it as minimally convex when compared to its neighbors (ie, try to make a sphere) and the holes are the spaces inside of the object where the object isn't (fuck that's also unclear). Like a mug is topologically the same as a donut.

Anyways, both the urethra and vagina are just concave spaces (divots) whereas the anus is a hole that connects to the face holes (mouth, nostrils, tear ducts). Assuming you define a hole as anything greater than 60 microns. Any smaller than that and the human body is basically Swiss cheese.