The way it's used on this forum, intellectual property, refers to characters, stories, or fictional worlds owned by an individual or entertainment company. The term has a modern connotation, because nowadays most fictional material has strict legal and financial attachments on how and when it can be used, but the same concept really goes back a long time. The only difference being that in previous decades, a lot more fictional material was available free-to-use in the public domain. In this way, the Walt Disney Company aquiring and using outside media franchises, like Star Wars and Marvel today, is no different from what Walt did in his time. The major difference now is that the negotiations for the user rights occurs between massive entertainment companies, whereas in Walt's day, he usually only had to negotiate with a single author or artist to aquire the rights (or nobody at all, in the case of public domain material).
Beside now all being familiar to the Disney Company under Walt, what do the Three Little Pigs, Snow White, Pinocchio, the Sorceror's Apprentice, Bambi, Dumbo, Cinderella, Sleeping Beauty, Treasure Island, Old Yeller, 20,000 Leagues Under the Sea, Swiss Family Robinson, Peter Pan, Alice in Wonderland, Winnie the Pooh, 101 Dalmations, Mary Poppins, The Wind in the Willows, The Legend of Sleepy Hollow, Pecos Bill, the Jungle Book, and probably other examples I'm forgetting have in common? None were original stories or characters dreamed up by the Disney Company. In several cases, the Disney version has become so dominant in pop cultural awareness that they have completely eclipsed their non-Disney origins (Winnie the Pooh and Mary Poppins particularly).
So, nothing new under the sun here. The biggest difference now might be that because the IP aquisitions come in a more ready-made form, the Disney company has less influence in reshaping them to fit the usual company aesthetic. For example, although the look of the Star Wars universe will always continue to evolve, I don't think we'll see it looking like a place where we might find Buzz Lightyear flying around.