I guess that would be a 'for sale by owner'...assuming that the seller would entertain someone making an offer on their home without a realtor involved. If a realtor has a contract with a seller, called a listing agreement, but the house is not on the Multiple Listing service, as an exclusive listing it can be called an inhouse listing.
If you are looking at being a party to a 'for sale by owner' I would always still insist on using an escrow company to execute the transaction and get title insurance to protect yourself. There are more court cases involving for sale by owner transactions than any other type of real estate transaction...but that's another discussion. Just don't EVER do a transaction without title insurance , or you are assuming a huge risk.