What does it mean if you have this in a C# code =-?

Can please someone explain to me the function this does?
Thanks in advance :)

... In C++ it means you're subtracting a value from the variables original value. I'm sure it's the same in C#.

But correct me if I'm wrong does it mean the same thing as -=? or no??

thats -= fred

Thank you DTScode for the help in the other post. Fredbill30 thanks for the attempt, I really appreciate it. But I found the answer, I was looking for. Thanks to all once again