Consortium

A conglomerate is a big company that owns a lot of smaller companies. Think: Disney owning ABC, Marvel, LucasFilms, etc. etc.

A consortium is a more...informal relationship. It's a group of companies that work together, but don't fall under the same ownership umbrella.

It's kind of the difference between your siblings and your friends. You're stuck with your siblings. They're part of your family. You're going to see them at every wedding, funeral, Christmas, Thanksgiving, and child's piano recital for the rest of your life. That's like a conglomerate (until the parent company starts selling off subsidiaries...then it's like the plot of a Lifetime movie).

Meanwhile, you get to choose your friends. And if you start to get tired of them, you can just stop texting. You might have some difficult-to-unravel arrangements (you moved in with your buddy and now you're both on the lease; you decided to split a timeshare with that girl from college; you're part-owner of three vending machines with the guy from your bowling team), but for the most part, you can take them or leave them as you choose. That's a consortium.

In the business world, these will often come together for marketing reasons. Different companies in a particular industry (beef, milk, etc.) will pool some money to promote their products. Or they might throw in together for lobbying efforts. A number of cross-company political action groups work for the interests of various industries.