In the expression \( 6 + 4(7 + 13) - 3 \times 5 \), the part \( (7 + 13) \) represents a sum, but in terms of its role in the context of multiplication, it can be described as a factor.
This is because \( 4 \) is being multiplied by \( (7 + 13) \).
So the correct word to describe \( (7 + 13) \) in this expression is factor.