Memo deductions/earnings are deductions/earnings that should not affect an employee’s pay. This is the theory, of course.
An example would be if an employee meant to pay for their delivered meal with their personal card but instead foolishly chose their company card to pay for it, and while they enjoyed their meal, they sat unaware of their mistake until the next day. Faced with the dilemma, they chose to have the amount taken from their next paycheck, and so, on the pay slip, there is a line item attached to a deduction mentioning why the deduction is taking place. Then the employee can continue their work in peace.
Except for the shame. The deep shame.