What's connection of "O" stated in the manual?

[patrick12345]

I'm the user of devialet 200 and just want to know that what's connection of "O" stated in the manual? 
(It's silver color which under the phono input) 

Per manual in Francais that this connection specified as "TERRE POUR BRAS DE LECTURE DE PLATIQUE VINYLE" but I don't understand Francais. Meantime, I can't find the english manual from the official website....

https://help.devialet.com/hc/en-us/articles/203402281-User-guide-of-120-200-250-400-800

Thanks to all

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