5.4.4.2 Absolute Objects In Program Memory

Any const-qualified object that has static storage duration and file scope can be placed at an absolute address in program memory.

For example, the code:
const int settings[] __at(0x200) = { 1, 5, 10, 50, 100 };
will place the array, settings, at address 0x200 in program memory.

An uninitialized extern const object can be made absolute and is useful when you want to define a placeholder object that does not make a contribution to the output file.