If it’s used to mean the whole front half, then the remaining part of the lamb is called the Hind End. If it’s used to mean the front third, then it’s used to mean the front third, then the remaining parts of the lamb are the middle, and Hind End.
It is considered better than the Hind Quarter which is the back part of the carcass.
If you happen to buy a whole Fore End including the breast, you can stuff it and roast it whole.
A whole front half of a lamb can weigh anywhere from 5 to 10 pounds ( 2 to 4 1/2 kg.)