Carry Flag (usually abbreviated as
CF) is part of the
Intel Flags Register (possibly of some other
status registers).
This flag is set when there's a carry out/into the most significant bit in an operation. This indicates an unsigned number overflow. This flag should be taken into consideration when working with unsigned numbers.
Example (in assembly):
mov al, 10000000b
add al, 10000000b
; CF=1 because there's a carry out of MSB
mov al, 00000000b
sub al, 10000000b
; CF=1 because there's a carry into MSB