what is difference between apartment terrace and patio?

Answer 1

In some cases, they may be used interchangebly.

However, "terrace" suggests an elevated patio, sticking out from the building proper. A terrace may be as little as a few inches is surface outside the apartment's sliding back door.

Answer 2

I always thought of a terrace as being basically little more than a fire escape, with a little wiggle room to put a chair or two and maybe a small table out there. Whereas a patio would be much larger.