>>13740340Three integrals.
Think of a simple 3d shape like a cube. You integrate once in one dimension and get the length of a single side. You integrate again and you get the length of the second side.
Multiply them together and you have a surface that is one face of the cube.
Integrate a third time and you get another length equal to the first two lengths. Multiply that by the cube face and you get length * width * height = volume.
Triple integrals allow you to do that same trick with basically any shape. You can do a bunch more fun shit like 3D Fourier transforms and whatever, but the gist of it is that you can perform integration in many dimensions. That's a pretty bland phrase until you start to realize all the shit that integration allows you to do.
