Here's a breakdown:

* Refraction is the bending of a wave as it passes from one medium to another. This happens because the wave changes speed as it moves from one medium to another, and the change in speed causes the wave to bend.

* Medium refers to the substance through which the wave travels, such as air, water, or glass.

Examples of refraction include:

* A straw appearing bent in a glass of water. Light travels slower in water than in air, causing the light to bend as it moves from the water to the air, making the straw appear bent.

* A prism separating white light into a rainbow. Different colors of light travel at slightly different speeds through the prism, causing the light to bend at different angles and creating a rainbow.