1. Diffusion is the net movement of molecules or atoms from a region of high concentration (or high chemical potential) to a region of low concentration (or low chemical potential). This is also referred to as the movement of a substance down a concentration gradient.
2. The passive movement of molecules or particles along a concentration gradient, or from regions of higher to regions of lower concentration.
https://en.wikipedia.org/wiki/Diffusion (1.); http://www.biology-online.org/dictionary/Diffusion (2.)
Author: Simon Waterstradt