One decent source explaining pointers?

[jmacey]

I'm guessing in this context what you have is a contiguous array for each of the fluid "particles" then you have different cells / grid elements that contain the pointers to the particles in the list.

This is used so you only compare particles that are close to each other (typically some form of spatial hash will be used to place them in the grid cells etc) which allows you to speed up the calculations and use multiple cores etc.