total function; sum function
Computing term for a function that calculates a total or sum, often in spreadsheets or databases.
I used the spreadsheet's total function to calculate the total sales.
合計 is the general noun for 'total' or 'sum', while 合計機能 specifically refers to the function or feature that performs the totaling.
Compound of 合計 (total, sum) and 機能 (function, feature).