Broadly speaking, somebody is statutorily homeless if they do not have accommodation that they have a legal right to occupy, which it would be reasonable for them to continue to live in. It would not be reasonable for someone to continue to live in their home, for example, if that was likely to lead to violence against them. The most visible of homeless people, those classed as "rough sleepers", are actually one of the smallest subgroups of "homeless". You don't have to be sleeping on the streets to be classed as homeless. There are many other situations in which the person is classified as being "homeless".

• Temporarily staying with friends or family
• Staying in a hostel or bed and breakfast
• Living in very overcrowded conditions
• At risk of violence or abuse in your home
• Living in poor conditions that affect your health
• Living somewhere that you have no legal right to stay in (e.g. a squat)
• Living somewhere that you can't afford to pay for without depriving yourself of basic essentials
• Forced to live apart from your family or someone you would normally live with because your accommodation isn't suitable

Those specifically sleeping on the streets can be referred to as roofless. Homelessness isn't only about sleeping rough on the streets. Housing insecurity and homelessness cover a wide range of situations. Many homeless people have a roof over their heads without having a proper home, because where they live is temporary, insecure, overcrowded, unsanitary or unsafe. 

As well as rough sleeping, street homelessness includes:
1. People who may have somewhere basic to sleep at night (such as a derelict building or squat) but who are on the streets during the day
2. People who stay in emergency hostels
3. Street-based sex workers who are vulnerable and homeless, but not visibly sleeping on the street

Street homeless people are those who routinely find themselves on the street during the day with nowhere to go at night. Some will end up sleeping outside, or in a building not designed for human habitation, perhaps for long periods. Others may sleep on sofas, friends' floors, hostels, night-shelters, squats, or spend nights in prison or hospital. Many street homeless people will alternate between sleeping in some form of accommodation and having to sleep rough. 

Homelessness affects a wide variety of people. Some groups of people are more vulnerable to homelessness because they have fewer rights, particular needs or are less able to cope by themselves. These include: young people leaving home for the first time; old people; people with; children; people with physical or mental health problems; people on benefits or low incomes; people leaving care; ex-prisoners; asylum seekers and refugees.

People become homeless for many different reasons. These include: being evicted by your landlord; losing your job; health problems; relationship problems; a disaster such as fire or flooding. 

It is often hard to measure homelessness, as people move from place to place, or keep themselves hidden from public view. For some it can be temporary problem, with people experiencing episodes of homelessness in between more settled periods. For others it can be more long-term. Homelessness can affect people from all backgrounds, but some communities are disproportionately affected. For example, in 2008/09, black and ethnic minorities represented 27 percent of all households found to be homeless in England despite making up only 11 percent of the total population.

64,000 homeless households in England were living in temporary accommodation arranged by local authorities at the end of March 2009. Just over 49,000 of these households had dependent children. Under homelessness legislation, if you are eligible, homeless and in priority need, your council has a duty to provide you with housing. This may entail a stay in temporary accommodation until a settled solution is found. If you are not considered to be in priority need, your council has no legal duty to provide you with accommodation, although it must provide you with advice and assistance to find your own accommodation. Temporary accommodation can be:
1. The local council's housing stock
2. Private rented sector stock
3. Short-term housing leased from private landlords
4. Hostels run by councils or registered social landlords
5. Bed and breakfasts or hotels

Charitable organisations also provide hostels and night shelters for single homeless people. Due to the current shortage of social housing, many homeless people can remain in temporary accommodation for several years before they're rehoused. Those unable to access temporary housing may have to make other short-term arrangements, such as staying with relatives or friends.