photoshop - What's the difference between saturation and vibrance in Lightroom?

Both options affect colors in a similar way, but I can't figure out the difference.

Answer

Saturation boosts all colours by the same amount whilst vibrance aims to boost the least saturated colours whilst leaving already saturated colours where they are.

The intent of increasing vibrance is to increase the apparent colourfulness of an image without overdoing parts that are already saturated, e.g. skintones.