Remains are what is left of something, or a dead body. Roman remains, human remains, the remains of the meal.
It is always plural, and in the sense of a body it is the word police and coroners use because it is neutral about identity and condition. Archaeological remains are protected by law in most countries. Note remain, the verb, beneath it.
1nounremainsWhat is left of something.
“Archaeologists found the remains of a Roman villa under the car park.”
remains is what is left.