It's the volume element in 3 dimensions, equivalent to dx dy dz, or whatever the volume element is in whatever coordinate system you're in (spherical, cylindrical, etc.). It's a Calc III topic. Here
So I'm working on a research project for my physics professor and although I'm a physics and math major, he's giving me a few problems with mathematical concepts that's beyond what I've taken so far. Here is the latest integral he is having me solve:
I haven't solved integrals that have looked like that with the d^3r term. What do you refer to this concept as (so I can know what to look for in order to study it)? And does anyone happen to have any resources where I can read up on solving them?