It’s stuff that overwhelms you when you look at it.  It’s stuff that’s in a tangle, or poorly organised (like a bookshelf with books and papers everywhichway); it’s that box of stuff you’re going to sort through “one day”; it’s that bag of clothes to mend, alter, use to cut a pattern from; it’s that box of bits and pieces in the garage that might come in useful one day.
It’s the plastics cupboard that you keep shoving things into and slamming the door thinking “I’ll get to that cupboard on the weekend”. It’s the linen closet that won’t close properly because there are too many old blankets, sheets, disused pillows, threadbare towels and stained tablecloths, it’s the kitchen table that’s covered in papers and books to the point where you can’t eat at it.

It’s the sight of the house in a disorder that you can’t clear, so that when you come home after a day’s work you sigh, avert your eyes and plop down in front of the television, too enervated by your clutter to do any of the things you really want to do but don’t have space for (like hobbies, or mending).  It’s all of the things I have just described (would it surprise you to know that all houses have them?) that you see, either physically or in your mind’s eye; that overwhelm you and make you sigh and make you tired just thinking about doing something about them.

(This is an extract of my book , there's more to a
definition of clutter - lot's more!)