Definition
In phonology, a natural class refers to a set of phonemes (sounds) that share distinctive features. Natural classes are made up of the fewest number of distinctive features possible to describe a set of sounds. Natural classes allow linguists to make generalizations about sounds based on how they are related in terms of their shared distinctive features (Zsiga, 2013).
Natural classes are based on articulatory and acoustic features, such as manner, place, voicing, etc.
Bellow is a chart representing common groups of natural classes based on their shared, (i.e., [+]) manner distinctive features.
INLP Linguistic Glossary 
