Hello,
I'm trying build an intercom system to use in our UTV. I found this circuit but I don't understand what the LS input is and where it comes from.

Thanks for you help.

 

hi TF,
Welcome to AAC.
Usually the abbreviation 'LS' refers to Loud Speaker.
So LS is where you connect the intercom speakers amp circuit
E

Please post a link to the design web page, the circuit is not a complete intercom project.
Updated:
https://en.wikipedia.org/wiki/Voice-operated_switch