What does this sentence mean? Can explain me more clearly.

I don't do Java, but I think this relates to variables that you have set globally, as opposed to locally (i.e. in functions, procedures, etc). So, you can use a global variable without declaring it again in the functions/procedures.

I did some Tcl, and I always have to declare my global variables, otherwise, the variable is treated as a local variable which goes to garbage once the procedure is executed.