Is there a difference between underweight, underfed and emaciated

I was just wondering, cause i am on the line between underweight and healthy according to my body mass index thing, the thing is though i eat alot and although most of what i eat is shit i still eat alot.
And how far does it go to be called emaciated? between my breast plates you can not really see the bone but i can feel it easily but my solar plexus is clearly visible also i sort of have a six pack but i dont really work out

I'm sure you're fine. If you're really concerned, go ask your doctor.

You would just know the difference if you were emaciated.

You eat way less than you think you do, trust me.

BMI index is outdated and often inaccurate but if your worried about your condition then you should see a doctor.