Add Definition
In mathematics, add or adding is defined as summing up two or multiples digits to obtain a new total value. Or in other words, to insert a particular quantity with the other to evaluate the total or whole amount is known as add or addition.
In addition, the symbol used to represent "add" is "+" For a more precise understanding, let us have some examples below:

One litter of milk is added with one liter to make two liters.

When 5 is summed with 3, the total add made by two digits will be 8.
Note:
To know more about it, you can use our Addend Definition.