Clutter is the objects and things that you keep hold of thinking that it might be used or come in useful one day!
What we tend to do is store things away in the loft or attic or in the cupboard under the stairs and keep them there for months or even years because that day might come when we actually need that item and use it.
Unfortunatly that day very rarely comes round and things tend to get piled on top of each other to bursting point! What happens next is that over time you notice how hard and how much longer it is taking you to simply give your home a quick tidy up, what used to take an hour is now taking most of the day!