What does this at sign mean?

The Schläfli symbol is a part of geometry, used to represent the shape of polyhedra.

By learning phonetic symbols, accurate pronunciation becomes possible.

Can you tell me the phonetic symbol of this word?

The bass clef is one of the basic elements of music.

Reading clefs is difficult.

He is an expert in semiotics, and his theories are very profound.

Semiotics is the study of signs and symbols used in society and culture.

My personal thought is that everyone should be treated equally.

When I first met her, I introduced myself saying, 'I am Japanese.'