Accrued interest is the interest to be paid by the bond buyers to the sellers of the bond.
The interest rate of a bond fixed in the coupon will be distributed to the holder of bond at certain interest payment dates. After such an interest payment date, a new interest period begins. In case bonds change hands during an ongoing interest period the owners, interest claims have already incurred and will be paid to the bond buyers at the next interest payment date. Therefore, they have to compensate the sellers accordingly. This interest claims are referred to as accrued interest and added to the purchase price.
The accumulated accrued interest can be calculated using this formula: Accrued Interest = Coupon * days since last interest payment divided by 360.
When it comes to dirty prices, interest payments are suspended, therefore no accrued interest can be claimed. There may be various reasons for this, such as the insolvency of the issuer.
You will find the current accrued interest on the respective bond data sheets on bond boerse-frankfurt.de.