Slavery is defined by Merriam Webster as "the state of a person who is a chattel of another." Despite being a well-known phenomenon, it is difficult to precisely define. Significant debates continue to rage over whether slavery is merely historical or whether it continues till this day in certain forms.
The scholar and historian Dr. Jonathan AC Brown has described the various definitions that have been proposed for the concept of "slavery." He argues that there is no single all-encompassing definition that works in all times and places - each definition has its shortcomings one way or another. In addition to Dr. Brown, other scholars have noted the difficulty of defining slavery; for example the scholar of slavery in Western civilization David Brion Davis has said, "the more we learn about slavery, the more difficulty we have defining it."
Refusal to define: slavery by recognition
According to this point of view, instead of giving an actual definition of slavery, we can simply say that slavery is known when recognized. If we see a particular scenario and it seems like it's slavery, then it probably is, and if it seems OK to us then it probably isn't slavery.
Dr. Brown points out that there were many instances of slavery that wouldn't look like slavery to the modern eye - for example, many of the Ottoman grand viziers were legally slaves.
Slavery as lack of freedom
Along with slavery-as-property, this is one of the most common definitions of freedom. It simply states that a slave is one whose freedom is involuntarily restricted by another human being. However, Dr. Brown points out that one's freedom is constantly restricted by other people all the time - by family members, coworkers, teachers, and so on. Thus there is no dichotomy between being "slave" and "free," rather the amount of freedom one has is always waxing and waning depending on the circumstance.
Dr. Brown also writes that some slaves attained more freedom after becoming slaves. For example, the Ottoman janissaries acquired land and political power which allowed them the freedom to do more things than they would have as peasants.
Slavery as property
Defining a slave as a human being as the property of another human being is one of the most common and straightforward definitions of slavery. In fact, this definition has precedent in multiple legal traditions. However, this definition is complicated by the fact that "property" is also a legal abstraction that's not always straightforward. Furthermore, in many past civilizations that had allowed slavery, the slave was given rights that a piece of property does not have - for example, a master could not kill his slave or even beat him.
In addition, activists who are working to abolish what's been termed "modern slavery" (see below) have conceptualized slavery as existing in contexts where the enslaved individuals are not the property of their masters, at least not in a legal sense. This further complicates the definition of slavery as human property.
Slavery as class
According to this definition, slavery is defined as a class of marginalized, subdued people. In nearly all pre-modern societies, there is a class of people that are distinct from the rest in terms of having less rights and so on, and while the specifics vary from civilization to civilization in a broad sense these classes can be referred to as "slaves."
The limits of this definition becomes clear when we societies where there were slaves who had a higher social status than many free people. For example, in India under the caste system slaves were above the lower castes in the social hierarchy. Furthermore, there are blurred lines between slave and free when looked at through the lens of class - which category do serfs, indentured servants, and debt servitude belong to? Thus, this definition can make slavery even more difficult to define and pin down.
Slavery as violent coercion
In recent times, activists against "modern slavery" have advocated for an expanded definition of slavery, one that focuses not on the legal status per se but rather the exploitative, coercive nature of many relationships. They focus on things like human trafficking, forced marriage, and laborers who don't have many rights. In these instances, the person being enslaved doesn't have the ability to walk away from the relationship if they want to.
This definition, however, might end up classifying large swaths of people as slaves who otherwise might be thought of as free. If someone doesn't have the ability to obtain a divorce from their spouse, they are technically forced to be in a relationship with them - does this qualify as slavery? In addition, there are examples in history of people choosing to become slaves, such as people so ridden with debt that they chose to sell themselves into slavery as an escape. One might move the goalposts by saying that this choice wasn't made in a free context, but ultimately no choice is. Thus, focusing on coercion to define slavery can lead to contradictions and unresolved issues.
As noted above, in recent decades a new movement has arisen primarily in the West which claims that slavery was never actually abolished, it was only abolished in a legal sense and the institution itself merely changed forms. The movement advocating for this viewpoint is called New Abolitionism, and the phenomenon they're fighting is called New Slavery, Modern Slavery, or Modern-Day Slavery.
Examples of phenomena they claim are modern-day forms of slavery include human trafficking, forced marriage, laborers who don't have rights, and private prisons. It should be noted that the New Abolitionists are not making an analogy - they don't say that these things are merely like slavery, rather their claim is that they are slavery.
- Brown, Dr. Jonathan. Slavery & Islam (2019).