outsider
A person who does not feel part of a group.
An outsider is someone who doesn't belong to a particular group, or who feels separate from it. In a new school, you might feel like an outsider until you make friends and learn the routines that everyone else already knows. Someone who moves to a small town where most families have lived for generations might remain an outsider for years, even if people are friendly.
The word can describe literal exclusion: a student not invited to join a lunch table is an outsider to that group. But it also describes a feeling. You might be technically part of a team but still feel like an outsider if you don't share inside jokes or if others have known each other much longer.
Being an outsider isn't always negative. Sometimes outsiders see things more clearly precisely because they're not caught up in a group's assumptions. A new student might notice that a classroom rule doesn't make sense, while students who've been there all year never questioned it. Scientists and artists often describe themselves as outsiders, viewing the world from fresh angles.
The opposite of an outsider is an insider: someone who belongs, who knows the unwritten rules, and who's part of the inner circle. Most people experience being both at different times. It can help to remember what it feels like to be an outsider when you find yourself on the inside.