The static Storage-Class Specifier
A variable declared at the internal level with the static storage-class specifier has a global lifetime but is visible only within the block in which it is declared. For constant strings, using static is useful because it alleviates the overhead of frequent initialization in often-called functions.
Remarks
If you do not explicitly initialize a static variable, it is initialized to 0 by default. Inside a function, static causes storage to be allocated and serves as a definition. Internal static variables provide private, permanent storage visible to only a single function.