The fuller answer
Loneliness is the feeling that connection is missing, even when other people are physically nearby. A person can have few friends and feel content, or many contacts and feel deeply alone.
School transitions, moving, disability, family stress, bullying, identity questions, social anxiety, depression, and online comparison can all increase loneliness. It is not proof that someone is unlikeable.
Connection usually grows through repeated low-pressure contact rather than one dramatic conversation. Persistent isolation, hopelessness, self-harm, or feeling that nobody would notice if you disappeared deserves prompt help.