I've never heard of the term 'individual contributor.' Can anyone clarify? As I understand teams are built from managerial roles and "worker" or technical or

I've never heard of the term 'individual contributor.' Can anyone clarify? As I understand teams are built from managerial roles and "worker" or technical or engineering roles. If it has to be a three tier system instead of two, it (typically) consists of a manager, then one or more tech/team lead(s), then engineer(s). I'm not sure which one of these are individual contributors. (or aren't they all?)