Well, it could be a number of things,.......could be a a hard fecal lump, could be a tumor, or an impaction of some sort, it's impossible to say over the net. But if it isn't passed within the next couple of days, I would STRONGLY suggest that you take it to a vet, he/she is the ONLY one who can "fix" it.
If this is ignored and left untreated, the snake could easily die, so it would be PARAMOUNT that you take care of this with a vet visit if the lump is not passed very soon.
It's always a good idea to check for these things, spinal kinks, over-all muscle tone, etc... before purchasing an animal.
Good luck with the animal, and I hope it does well!
best regards, ~Doug

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"Better to be silent and thought a fool, than to open mouth and remove any doubt!"