What does the term "contraband" refer to?

What does the term "contraband" refer to?

You may have noticed, or may notice, after reading this note, that the characters use the seemingly innocuous term "contraband" or "contrabands".

For those who don't know, the seemingly innocuous term "contraband" refered to the human beings who were held as slaves, in the breakaway states, who escaped, and made it to the Union held areas, or who had lived in a region the Union captured.

Weren't they automatically free, once they made it to the Union areas? My understanding is that they were able to enjoy a measure of de facto freedom, they were not, until the Emancipation Proclamation, one hundred percent free. My understanding is during the decades prior to the civil war southern legislators had been able to convince Congress to pass laws that authorized bounty hunters to go to free states to recapture runaway slaves, who weren't fully free until they made across the US border into British North America. Upper Canada, what is now Ontario, was the first jurisdiction in the British Empire to outlaw slavery, around 1790.

Does this mean that if some or all of the secessionist states had negotiated a peaceful return to the Union that those individuals the Union classified as contraband, while at war, might have faced being involuntarily returned to their former bondage? I dunno. At some point Lincoln's policy became unconditional surrender, which suggests no slave state could negotiate a return to the Union. But if Lincoln had died earlier, or the war had gone on longer, a new President could have dropped the unconditional surrender, putting the fate of the so-called "contrabands" up in the air.