Are Ghosts Biblical?

I cannot find anything in the Bible mentioning them, yet I have seen things and felt things that I can only assume are ghosts. I have spoken to other Christians on this subject. Some believe they simply do not exist, others that they are demons and disguise, which is scary to think about, and some believe in them. If ghosts are not mentioned in the Bible, then what are they? If they are, why are they still here after death when the Lord has places for us to go after death? Sorry if I worded this badly; I am not very good at organizing my thoughts sometimes. I hope one of you can answer this.