Does FLAC is a compressed format?
FLAC is compressed but the compression type is different from MP3, M4A, etc. Think of it this way. You have two pieces of clay. Unfortunately, you must carry it in a box. You just happen to have two boxes. One is a bit smaller than the first piece, so you just squeeze the clay together until it fits in the box. The second box is much too small, though. So, you rip off pieces of the clay and throw them away, then squeeze the remaining clay together until it fits in the box.
The first box represents FLAC, i.e., you're not throwing anything away. The second box is MP3, i.e., you are throwing something away.