Imagine you’re telling a story to coworkers about a road trip you took a few years back. You set up the context of the trip, including where you were going, why you were going there and who was in the car with you. But as you list out the people in the car, you realize you can come up with two of the people, but not the third.
You pause to give your brain a chance to come up with the name of that third person. As you think, without realizing it, you let out an "umm…" for a good, full second. Then, when the name comes to you, you say it and move on with your story.
That "umm" is what we call a "filler word."
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