That's known as a short block. When you get the crank, rods, and pistons and the bearings that's known as your rotating assembly. Forged internals are just a stronger type of the rotating assembly versus the factory cast parts. Forged is highly recommended if you plan on running either forced induction or a higher compression ratio, though not so much for the compression ratio.
Sold - Black 2000 Mustang GT, gone but definitely not forgotten
- Silver 2007 Corvette
Current - DHG 2001 Bullitt