what is difference b/w refraction and rarefaction?

Hi Aman!

Refraction:

The phenomenon of bending of light (or other waves) from its straight line path as it passes obliquely from one transparent medium to another is called refraction of light. It occurs because the speed of radiation is different in different medium.

Rarefaction:

Sound waves travel in series of compressions and rarefactions. Compressions are the areas of high pressure and   low pressure regions in sound waves are called rarefactions.

Cheers!!