Hi Billy I can't say for sure what this lump is, but I'm inclined to think it's a type of hernia called an 'incomplete closure'. It's fairly common in puppies and can be caused at birth by the momma dog being too vigorous about cutting the umbilical cord - it can also be a genetic weakness.
What happens is the muscles in the abdominal wall don't quite mesh as they should, leaving a weakness or gap between them, usually around the belly button area.
The lump that results is where some fat drops down through the opening and bulges outwards. Generally you will be able to push this little lump back through the gap in the muscle wall and it won't bother the puppy.
However, occasionally some bowel will drop through the opening rather than just fat, and if this gets caught between the muscles and can't be pushed back into the abdominal cavity it can cause serious problems.
Fat can get trapped too, but this isn't so serious.
I strongly suggest that you have your veterinarian check your puppy out to see if this is what is causing the lump, or whether it's something else. Often this type of hernia will close up as the puppy grows, if it doesn't and your vet recommends surgery it's a very simple procedure.. just a couple of stitches to hold the muscles together. It can be done at the same time that a puppy is being spayed with no problem.