TRUNC is a worksheet function in Excel that allows you to truncate a number to a certain number of decimal places. It is useful when you want to round a number down to the nearest whole number or to a certain number of decimal places.

To use the TRUNC function, select the cell in which you want the result to appear and enter the following formula:

=TRUNC(number, num_digits)

where number is the number that you want to truncate and num_digits is the number of decimal places that you want to keep. For example, if number is 12.345 and num_digits is 2, the result will be 12.34.

You can also use the TRUNC function to round a number up or down to the nearest multiple of a certain number. To do this, enter a negative value for num_digits. For example, if number is 12.345 and num_digits is -2, the result will be 12.35 (rounded up to the nearest multiple of 2).