HPSM variable starts with $ in forms value list

Dear Team,

Can any one suggest in how many ways we can identify the variable which is defined in one HPSM form which is starting with $.

this variable is deined in value list in some forms.

Please provide any documentation if any for more details about this type of variables.

https://docs.microfocus.com/SM/9.61/Hybrid/Content/programming/system_language/concepts/variables.htm

I find some information like these variables will be called as thread variables in MF site, but need more clarity and more information on this apart from that like how many places it can be defined , how many ways it can be called etc.

Thanks

Anjaiah.