Functions in Optislang

What is the meaning of these functions needed in the objectives definition in Optislang

The link below has the list and the definition of all the functions in Optislang, e.g. $SIG_MAX_Y:

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v251/en/opti_ug/opti_ug_macros_signal.html?q=%24SIG_MAX_Y