A bed & breakfast and guest houses have several things in common.
A guesthouse is generally a larger property with more than 5 bedrooms.
It's basically a small hotel and are usually owner-operated. The host might live on the premises.
Breakfasts are served in the morning. Other meals such as dinner are often provided. Larger guest houses have common guest areas such as a lounge and dining room.
A bed and breakfast room is part of a private family house.
B&B's are generally smaller than a guest house, and normally accommodate no more than 6 guests. There is no restaurant or bar. Breakfast is served in the bedroom, a dining room, or the host's kitchen. Most of them are reasonable priced.
Usually the owners live on site and no other meals other than breakfast is served. In fact, you are a guest of the family. Most rooms are en-suite, but you might find also shared bathrooms in some older houses.