This is a recently INVENTED word which has appeared in the mass media, perhaps from the Millbank spin machine, in an attempt to justify attacks on the right of refugees to flee oppression, torture and death. It did not exist until about a year ago. It is used as an excuse for persecuting refugees and those who transport them, by likening the latter to drug and arms "traffickers" (although genealogically, to "traffick" simply means to move something from one place to another - in which case all commercial pilots, bus and train drivers and people who take passengers in their cars are strictly speaking "people traffickers" - it is linked to the word "traffic", used to refer to lots of cars etc. in one place; this use, however, is archaic, and to traffick now means to smuggle illegal goods).
It basically means that the people who use the word think that people - especially black people - are THINGS which can be OWNED and therefore TRAFFICKED like drugs and arms; worse still, that people are ILLEGAL goods to be trafficked and owned. Its use is evidence of the barely concealed racism of the government and the corporate media as well as all the sheep who buy into the filth they spout.
It has become popular partly because of a lot of publicity surrounding sections of migrancy which are run by organised criminals and involve the establishment of sex slavery and forced labour. However, the laws brought in against "people traffickers" are typically aimed at ANYONE who transports migrants, including refugees, and so could even apply to heroic people such as human rights activists who help people flee oppression.