Drew, an oceanography graduate student, writes:

“This, on my leg, is the incompressible form of the conservation of mass equation in a fluid, also known as the continuity equation. When people ask what it means, I say it defines flow. Sometimes I say it means you should have studied more physics, but that is only when I am feeling like being funny. What it means in more detail is that, for an incompressible fluid, the partial derivative of the velocity of the fluid in the three spatial dimensions must sum to zero. It therefore concisely states the fundamental nature of a fluid.”My advisor took this picture, and I swear he is obsessed (in a good way) with this tattoo. He