A stranger means anyone personally unknown to the observer, however well known by reputation.

Evidence

My use of the term is different from any of these. By stranger I refer to any person who is personally unknown to the actor of reference. Thus, as we have seen, while a celebrity is personally known to many persons, the majority of these are not personally known to him. In this sense, to all of us most of the world’s three billion people are strangers. — Lyn H. Lofland, World of Strangers_ Order and Action in…, 109

Categorization

• DEFINE: Lofland’s working definition of ‘stranger’ centers on personal unknownness to the actor of reference, not on difference or loneliness.
• XREF: This operationalizes the person to whom Simmel’s blasé attitude and Lofland’s own stranger-typing applies; also relates to the classic Simmel essay ‘The Stranger’ which uses the term differently, as the wanderer who comes today and stays tomorrow.