If you have stuff that can be useful and/or used by someone else, they you are a stockpiler. If you can easily part with your possessions you are generally ok. If you can go through a pile of stuff, divide it into keep and toss, you are doing good. But when the entire pile of stuff becomes "keep"... well...

If you keep stuff that has no possible value to anyone but you, and the reasons you are keeping these items seems odd to other people, and there is no way in God's green earth you are going to part with your stuff, then you are a hoarder.

The people on A&E are sad examples of typical cases.

I keep stuff that I can see someday using. However I also know that some things have outlived their usefullness and out they go.