Soul Trafficking (sometimes called slavery, people trafficking, milking, or specifically [Race]-Trafficking) was the archaic practice of taking any living creature and subjugating it to the (usually) unquestionable will of another creature.
Trafficking of souls was popular during the Holy War, and could even be called commonplace in the earlier BR era, but the practice died out in the early PR era with the continuation of the Realm War. By the time that the kingdoms of the realm fell in the 300s PR, trafficking had become so rare that many people in the realm simply believed it didn't exist, though pockets of evil would always try to move precious lives against their will, adventurers and heroes had become so widespread that the practice became too risky to attempt, even in the shadows.
History
Historic Soul Trafficking
The Shinardu of the Troverth Dynasty were famously a class of artisans who made their money trafficking both entire individuals, as well as "rare" parts such as Satyr Horn, Orc Skull, Human Horn, and other supposedly useful goods.
During Realm War I, one notorious trafficker of "exotic" souls (a word used to make Fey creatures sound more exciting than they were) was Asar Partui. Asar was famous for taking war criminals found in the Fey Front and taking them across the realm, trapped in a Ring of Marquee against their will, and sold off to highest bidders anywhere from Pteris to Amusa (unsurprisingly, selling elven and fey slaves was an unpopular concept in the northern continents).
Urban Soul Trafficking
The city of Galik was known to harbor a massive underbelly where the trafficking of any souls, including children and elders, could be found if you knew the right place to shop. One hero, Orris, dedicated the rest of his life from the moment he stepped foot in Galik tracking down trafficking criminal guilds such as the Shadowguild.
Modern Soul Trafficking
Though the modern world believed itself to be rid of slavery and trafficking, pockets of slavery still existed in otherwise seemingly civilized locations. Sneerwell was an example of modern slavery, where the city kept a tribe of Orcs that was raised from birth to tend to the city's agriculture. Many Orcs of Sneerwell were liberated by Sick of this Shit in 693 PR.