What does the F() do exactly?

[quote author=Coding Badly link=topic=91314.msg685894#msg685894 date=1328909536]

ninja2:
Could this F() syntax be used in place of rather cumbersome:
strcpy_P(buffer, (char*)pgm_read_word(&(str_table[index])));

This may help...
http://arduiniana.org/libraries/flash/[/quote]

can you clarify the origin of the F() syntax, is it from Mikal Hart's Flash library, or is it part of C or the standard IDE ?