Then the result $a + b$ is referred to as the sum of $a$ and $b$.
Note that the nature of $a$ and $b$ has deliberately been left unspecified.
Consequently, at that level, all such arithmetic lessons are often referred to as sums.
To those with math anxiety, the very word sums may be distressing, while in the humour of children's comics, a popular punishment for a child would be to be sat down at a desk in front of a book titled hard sums.
- 1974: Murray R. Spiegel: Theory and Problems of Advanced Calculus (SI ed.) ... (previous) ... (next): Chapter $1$: Numbers: Real Numbers: $1$
- 1981: Murray R. Spiegel: Theory and Problems of Complex Variables (SI ed.) ... (previous) ... (next): Chapter $1$: Complex Numbers: The Real Number System: $1$