The Meaning Behind Doug Emhoff Tattoos

I am currently learning about the concept of convolution between two functions in my university course. The course notes are vague about what convolution is, so i was wondering if anyone. Please provide additional context, which ideally explains why the question is relevant to you and our community.

Background and motivation, relevant. I have read that an infinitesimal is very small, it is unthinkably small but i am not quite comfortable with with its applications. My first question is that is an infinitesimal a stationary value? In mathematical notation, what are the usage differences between the various approximately-equal signs ≈, ≃, and ≅? The unicode standard lists all of them inside the mathematical.