I am coming more and more across places which call themselves 'hostel' in their name, but which have more the character of a B&B/Guest House/Pension.
Hostels do of course vary over a wide range of standards from a simple country farmhouse with self-catering and 8-bed dorms only, through to facilities with dorms and private rooms with TV and en-suite and all meals available.
The British tourist bureaus have definitions which distinguish between 'Hostel', 'Bunkhouse' and 'Camping Barn' in terms of facilities and awarding stars. But I think we should agree on a definition of 'Hostel' with worldwide application. This forum seems a good place to determine such a definition.
1) You might say: To be a hostel, there must be dorm beds. I would say: Not quite so. What is essential is: They don't charge more for an individual traveller than for one of a couple. I think indeed this is the crucial definition. So if a facility charges, say, £16 per person for a couple in a double room, and £16 for an individual and chooses to put him in a single room, they are eligible. But if they charge £18 for an individual traveller, they are NOT ELIGIBLE.
2) A common room. Some hostels fail on this -- there's one in Edinburgh that brings your breakfast to your bedroom and has no common area. Some are pretty poor, with a sofa and chair in the reception hall having to suffice. Some have a common room with chairs in a semicircle facing a TV, which is not very congenial. Some have a common room which is so placed that people don't bother to discover it.
3) A self-catering kitchen. I would like to make this an essential criterion, but unfortunately that would leave out many facilities, some of them excellent in other ways. In some countries this is not normal at all. Some have a limited kitchen, eg microwaves and 2 stools to sit at. Some are miserly with equpment -- 2 battered pans, no soup bowls, no dishwashing soap -- and I've seen kitchens with no equipment AT ALL!
It is quite common now for hostels to try to cater for different types of traveller from the backpacker to the family and business visitor, and the YHA does this. New facilities call themselves 'hotel and hostel' in the hope of attracting all types, but they haven't always grasped what a hostel really is. For example, they seem determined that everybody wants privacy.
The definition I use is:
A hostel must provide budget-price accommodation, including 1-night stays, must welcome individual travellers and must not charge them more than a member of a couple or group. A hostel must have a common room where guests can sit and chat, or eat communally.