Usually, factorization or factoring means writing a number (or another mathematical object) as a product of minor or more uncomplicated objects of the same kind.
Given -x-5 is a linear expression.
For factorizing, first, make the coefficient of x positive. For this take -1 common.
⇒ -x-5 =
Now take the greatest common divisor (gcd) of absolute values of coefficients in x+5.