I think its very obvious what is slavery so lets discuss just global slavery index -
What is Global Slavery Index
Global Slavery Index estimates the number of people in modern slavery in various countries and come with their relative ranking in terms of modern slavery practices happening in respective geographies. It is a tool for citizens, non government organisations, businesses and public officials to understand the size of the problem, existing responses and contributing factors, so they can build sound policies that will end modern slavery.
What is the Information contained in the Global Slavery Index
What is the estimated prevalence of modern slavery country by country in terms of its population? How are governments tackling modern slavery? What factors explain or predict the prevalence of modern slavery? These are the main points covered in the Global Slavery Index
Who Prepares Global Slavery Index
Walk Free Foundation (a global organisation dedicated to ending modern slavery)