signed overflow
When a signed result is too big or too small for its width, so the stored answer has the wrong sign.
n-bit signed overflow occurs when the true result lies outside -2^(n-1)..2^(n-1)-1; for addition, exactly when both operands have the same sign and the result's sign differs.
Examples
In 8 bits, 100 + 50 = 150 doesn't fit in −128 to 127, and the bits read back as −106.
See also