Diffusion is a time-dependent random process causing a spread in space.

Diffusion may also refer to:

• Molecular diffusion, spontaneous dispersion of mass (distinct from migration, caused by an external force)
• Conduction of heat
• Momentum diffusion
• Diffusion equation
  • Heat equation
  • Schrödinger equation
• Eddy diffusion

• Anomalous diffusion, the movement of particles from a region of lower concentration to a region of higher concentration
• Diffusion MRI
• Diffusion (acoustics), sound waves
• Atomic diffusion
• Brownian motion
• Collective diffusion
• Facilitated diffusion
• Effusion of a gas through small holes
• Gaseous diffusion
• Itō diffusion
• Knudsen diffusion of particles from very small containers
• Osmosis, the movement of molecules through a membrane
• Reverse osmosis, a process to separate unwanted particles from a fluid
• Photon diffusion, an optical effect
  • Diffuse reflection, the reflection of light from an uneven or granular surface
• Reverse diffusion, the movement of particles from a region of lower concentration to a region of higher concentration
• Rotational diffusion
• Self-diffusion
• Surface diffusion
• Thermodiffusion

• Diffusion of innovations within a society or a culture or between them
• Lexical diffusion within a culture
• Trans-cultural diffusion of culture items between cultures

• Diffusion (cryptography), the spreading of influence of bits in a cipher
• Error diffusion in image processing
• Diffusion model in machine learning media or text generation.

• Diffusion (business), the process by which a new idea or new product is accepted by the market
• Diffusion line, a secondary line of merchandise created by a high-end fashion designer
• Diffusion Pharmaceuticals, a drug development company
• Diffusion process, in probability theory the solution to a stochastic differential equation
• Diffusion of responsibility
• Society for the Diffusion of Useful Knowledge
• Diffusion Science Radio Show, a science radio show and podcast on 2SER in Sydney
• Diffusion Records, an independent record label
• Sound diffusion, a performance practice in electronic music

• Diffuser (disambiguation)
• Diffuse nebula
• Migration (disambiguation)