Ambergris is often referred to as "whale vomit", but that's not really correct. A more accurate analogy would be to say that ambergris is like the whale equivalent of a hairball. It's produced in the whale digestive tract, possibly to protect intestines from the sharp, pointy beaks of squid — you'll often find squid beaks embedded in the stuff. Most of it gets pooped out. But the big chunks of ambergris have to exit the other direction. In the human world, these lumps — which have the consistency of soft rock or thickly packed potting soil — are famous because we use them to make things like perfume. The ambergris washes up on beaches, people collect it, and sell it to make cosmetics.
Anyway, that's what usually happens. Recently, a dead sperm whale washed up on a beach in Holland and the conservationists who dissected it found a huge quantity of ambergris in the animal's intestines.
That news made me realize that I'd never actually seen a picture of ambergris before, so I went hunting around to see what the stuff looked like. That's a photo of a lump of ambergris, above. But it's not really indicative of what ambergris looks like all the time. In fact, as far as I can tell, the stuff comes in a wide variety of shapes and colors — ranging from stuff that looks like small brown pebbles to yellow-green globs covered in bubbly nodules. The diversity is worth perusing. This website, for a company that buys and sells ambergris, has several nice photos. And Google image search turned up a plethora of pics that really capture how different one lump of ambergris can be from another.