They are bad words, my friend, bad words. No, not like that.
Filter Words are words that you want to be rid of when you're editing. Once the story is straight and you are streamlining your delivery. They're the nasty words that don't need to be there.
I know this isn't helping. Hold on. I'll let the kittehs explain...
The one Filter Word that everybody has heard of is 'very'. You shouldn't use it. I was very hungry should be I was famished. You shouldn't be very anything. It is not eloquent, and we are about the words, and eloquent they should be.
So at the end of the draft, wherever you choose to do it, get out the find tool on the word processor, and find all the examples of very. And try to get rid of them. Make the work more eloquent. And it actually works. But there are many other Filter Words...
Do your characters look at things? Of course they do. Shut up. But, do you need to tell your reader that?
Bill stepped out of the trailer and looked at the reddened moon as it dropped below the horizon...
Bill stepped out of the trailer as the reddened moon dropped below the horizon.
See what I'm saying?
Little Timmy decided to have some bacon and went to the store.
Little Timmy went to the store to get bacon.
Jane Austen, angry at her mother for naming her after the author, noticed the way the blood splattered when the neck was punctured with a knitting needle.
The blood splattered as Jane Austen punctured her mother's neck with a knitting needle, for naming her after the author.
It seemed to Nettie, that it was humid.
It was humid.
Mostly, your Filter Words are Filler Words. In the examples above, you can see that what the Filter Word is saying, is already implied by the rest of the sentence.
So in the last piece I finished I went through the document looking for them. There were lots. I mean lots. These are just some to watch out for:
Thought; Saw; Heard; Look; Watched; Seem; Feel; Decide; Feel; Notice;
There are plenty to watch out for.