[Verginius Rufus]

Does this figure count only people who are actual slaves, or does it include "debt slaves" who are de facto slaves because they must work for a creditor and are never able to pay off the debt? Not people who have run up high credit card debts on items they didn't need, but poor peasants forced to borrow money at extortionate rates to avoid starvation.

[SeekAndFind]

By slavery,they mean people being treated as property who can be bought or sold.

The are deprived of the right to leave, to refuse to work, or to demand compensation.

Just read this from the above article:

“Islamic State has SOLD thousands of ethnic minority women into slavery, mostly to become “wives” to their fighters. Boko Harum in Nigeria has done the same thing.”

So, by their definition, our Western definition of “debt slavery” does not count.