Dear to whom may it concern,
I have a question about [color=red]'s.In the listening exercises 21/3 I saw this title but I don’t understand the meaning of it. It was [color=red]At the optician’s. Optician means expert of optical instruments who makes or fits optical lenses. What is the meaning of 's here?
With the best regard

Sometimes the possessive implies a place. In this instance, it would be the optician’s place of practice.

I’m at Sally’s. - I am at Sally’s house, apartment, etc.

[color=darkblue]Dear Mordant,
Thank you very much indeed for your complete explanation.
Sincerely yours