Loneliness is the painful feeling of being alone or disconnected from other people, even when you're surrounded by them. It's different from being physically alone: you can feel lonely in a crowded cafeteria if no one seems to understand you, or feel perfectly content reading by yourself on a Saturday afternoon.

Loneliness happens when there's a gap between the connections you have and the connections you need. A student who moves to a new school might feel intense loneliness in those first weeks, sitting at lunch watching everyone else talk with their established friend groups. Someone who loses a best friend to a move across the country might feel lonely because they miss that specific person and the unique connection they shared.

The word carries a sense of longing. When you're lonely, you notice you're alone and wish things were different, wanting to feel understood, valued, or included.

People often confuse loneliness with solitude, but they're different. Solitude is the state of being alone, which can be refreshing and peaceful. Loneliness is the unhappy feeling that comes from missing meaningful connection with others. A scientist working alone in a lab for hours might enjoy the solitude, but feel lonely if she has no colleagues who share her interests or care about her work.