1. The phrase "sum of" in mathematics means addition, not multiplication. 2. When you see "sum of" two or more numbers or expressions, it means you add them together. 3. For example, the sum of $a$ and $b$ is written as $a + b$. 4. Multiplication is indicated by terms like "product of" or using symbols like $\times$ or $\cdot$. 5. So, "sum of" always refers to addition, which combines quantities by adding them. 6. Remember: sum = addition, product = multiplication.