It is hard to define loneliness because it is a subjective experience, much like chronic pain. However, researchers loosely define it as a subjective deficit in the quantity and/or quality of social relationships, resulting in unpleasant feelings (one reasercher called the feelings “Gnawing distress without redeeming features”). Experts debate whether the definition should include awareness of the loneliness by the person. For an example of how someone may be lonely but not aware of it, think of the character Scrooge in Charles Dickens “A Christmas Carol”. Experts also classify loneliness as:

Loneliness can mean: feeling that you are unacceptable, unloved by those around you, not worthwhile, even if others don't share these perceptions; feeling alienated from your surroundings: lack the attachments that you had in the past; feeling that there is no one with whom to share your personal concerns and experiences; feeling that you are alone.

In addition to being subjective, loneliness is relative. Individuals seem to decide they are lonely based on some personal belief about how many relationships they should have. Those beliefs can be based on several things, including impressions from television shows, movies, and books. The beliefs may also be based on the individual's impressions of their peers' social lives. For example, people who are widowed before the age of 70 report more loneliness than people who are widowed after the age of 70, presumably because the death of a spouse is more common after age 70. A person may also be comparing their current social levels with their memories of how life used to be (accurate or not). However, these expectations are not permanent and as people age they often report being less lonely