Undergrad Diffusion & Effusion: What Is It?

[Viona]

I understand that diffusion is the movement of molecules from a region where concentration is high to one where it is lower.
This happens due to the molecular agitation which leads to frequent collisions and hence scattering of molecules.

But I do not know what is effusion. Any help? Thanks

 

[anorlunda]

Have you tried this? https://www.merriam-webster.com/dictionary/effusion

 

[Chestermiller]

Many people use the word effusion to describe convective transport.