Coupon is a specific amount required to be paid by the issuer to the bond buyer strictly according to the payment schedule. The coupon is paid strictly according to the rate of % per annum agreed on the Mosbirge website. Coupons can be paid monthly, quarterly, semi-annually, once a year.
The coupon amount accumulates daily from one payout to another. What happens if you bought bonds with quarterly coupon payments, for example, if a month has passed since the last payment? The buyer of your bonds pays you the Accumulated Coupon Income (ACI) and you receive it to the account. Next, the buyer will receive his share of the ACI by the time of the new payment of coupons, i.e. for the two remaining months.