Washington State Bill Of Sale What Exactly Does A Real Estate "Bill Of Sale" Mean?

What exactly does a real estate "Bill of Sale" mean? - washington state bill of sale

I am negotiating to buy a house with the current owner. For sale by owner. Do you want me to sign a contract of sale conditional on the purchase price and date, but I am not prepared to do. I'm not sure what the deed, and I fear that an agreement will be legally binding without any appeal to me.

He's in Washington State, USA. Thank you for your help.