Elementary question on const

From: Last Timer (dakshing64_at_yahoo.com)
Date: 01/30/05 

Date: 30 Jan 2005 11:31:14 -0800

I encountered the following code in Bruce Eckel's online book. Can you
please clarify what "const char* const data;" means? Thanks
//: C01:MyError.cpp {RunByHand}

class MyError {
const char* const data;
public:
MyError(const char* const msg = 0) : data(msg) {}
};

void f() {
// Here we "throw" an exception object:
throw MyError("something bad happened");
}

int main() {
// As you'll see shortly, we'll want a "try block" here:
f();
} ///:~