If it's hard to determine its shape and otherwise looks like a big blob of something, it's probably safe to call it a lump.
Jabba the Hut looks like a disgusting lump. So does the growing mound on your noggin where you walked into the glass door. And if you've been lumped together with a bad bunch, you might have been grouped with people indiscriminately. But all lumps aren't bad. Little old ladies put lumps of sugar into their tea. And that choked up feeling you get during a sappy movie? That's just a lump in your throat.