What does this "%SystemDrive%" mean

[RLGL]

When the % sign is used in the fashion as in the title , what does it mean? I see the usage in many places but have not been able to interpret it. I know nothing about programming language

THX

 

[ninaholic37]

I think it usually means C: in Windows

https://en.wikipedia.org/wiki/Environment_variable#Default_values

 

[RLGL]

Thanks, I learned something new today.