“Inmate” is a euphemism for “prisoner.” Prisoners are people held by force in places they don’t want to be — jails, prisons, juvenile detention centers (child jails), places like that.
There are a few different reasons you might want to call someone an “inmate” rather than a “prisoner,” even though the two words mean exactly the same thing. One is: Maybe you or someone you love is a prisoner, so to distract yourself from how horrible that is, you call the predicament by another name.
Or maybe you work for an organization that imprisons people — a police force, a government entity, or a branch of the military — and you’re hoping to convince yourself the prisoners don’t have it so bad. “Inmates” sounds friendly by comparison, almost like the prisoners could leave if they wanted to. They’re inmates. They’re fine. The system that brought them here is fine.
Here is another reason you might say “inmate” when you mean “prisoner:” Names are important. Maybe if you call people “inmates,” you’ll see their humanity a little more clearly than you’d see it if you called them “prisoners.” Maybe you’ll treat them with more respect.
It’s best not to jump to conclusions.