In other words, the company that supplies chocolate, in our candy bar example, buys from a company that grinds and roasts cacao seeds who, in turn, buys the seeds from another supplier. You get the idea. This type of within-industry market broadening is termed vertical. So, from this overly general viewpoint, we can lump direct , private, and vertical together. On the other hand, it's tempting to lump indirect and public with horizontal .
Travel services is the easy example.
Now, goggles off. There are, of course, lots of exceptions to this general clustering. Otherwise, we'd only need one level of distinctions, instead of three. This is just the tip of the exception iceberg, but I still think it's useful, as a mental starting point, to group these markets into the two clustered stereotypes. Finally, every market has buyers and sellers.