We all feel lonely from time to time. Feelings of loneliness are personal, so everyone's experience of loneliness will be different.
One common description of loneliness is the feeling we get when our need for rewarding social contact and relationships is not met. But loneliness is not always the same as being alone.
You may choose to be alone and live happily without much contact with other people, while others may find this a lonely experience.
Or you may have lots of social contact, or be in a relationship or part of a family, and still feel lonely - especially if you don't feel understood or cared for by the people around you.
The connection between loneliness and mental health problem
Feeling lonely isn't in itself a mental health problem, but the two are strongly linked. Having a mental health problem can increase your chance of feeling lonely.
For example, some people may have misconceptions about what certain mental health problems mean, so you may find it difficult to speak to them about your problems.
Or you may experience social phobia - also known as social anxiety - and find it difficult to engage in everyday activities involving other people, which could lead to a lack of meaningful social contact and cause feelings of loneliness.
Feeling lonely can also have a negative impact on your mental health, especially if these feelings have lasted a long time. Some research suggests that loneliness is associated with an increased risk of certain mental health problems, including depression, anxiety, low self-esteem, sleep problems and increased stress.
The mental health charity Mind has useful resources for loneliness on their website.