A big dumb object is basically something that is very large and not very smart. It's like a giant toy that you can play with, but it doesn't have any brains or intelligence. Think of it like a big rock or a huge spaceship that doesn't do anything on its own.
People like to use the term "big dumb object" for things that are so massive and complicated that they're hard to understand or explain. For example, if you saw a huge building with lots of floors and no obvious entrance, you might call it a big dumb object because it's hard to figure out what it's for or how to use it.
Overall, a big dumb object is just a cool-sounding term that people use to describe things that are big, impressive, and kind of mysterious. It's a way to capture the awe and wonder of encountering something truly massive and powerful, even if it doesn't have any brains or personality.