The ranks of homeschoolers are rising rapidly across every social strata, faith and ethnicity.

FORBES: Want To Tell The State To Stick It? Homeschool Your Kids

But the word "caste" is routinely used by government experts to refer to social strata in underprivileged Muslim communities.

WSJ: India Classifies More Castes as 'Backward' In Affirmative-Action Bid to Help the Poor

It binds together people from different social strata and ethnic background with diverse social practices, beliefs, professions and languages.

UNESCO: Culture

Recent international studies indicate that British social strata are a bit more flexible than America's but more rigid than in many European countries.

ECONOMIST: Class

It requires the selfless cooperation of many people from all age groups, social strata and backgrounds, promoting and encouraging teamwork and contributing to local harmony and conviviality.

UNESCO: MEDIA SERVICES

Society being composed of social strata a family will find its children in competition with children from families in roughly the same social-economic stratum, with roughly the same total amount of family income to invest in children.

FORBES: Demographic Decline and Investment Intensity in Children -- Observations on China and Japan

They found on average a 19% difference between the highest and lowest social strata in the risk of dying in each country and about half of the difference was due to the risk of being killed by smoking.

BBC: NEWS | Health | Smoking 'accounts for health gap'