b or price without addendum (price detail)
Former price detail "bezahlt": all orders were executed
B stands for "bezahlt" (German for "paid") meaning all limit orders at the noted price were executed (or price without addendum)
Price details were abbreviations which were published in floor trading with a price quotation and offered additional information about the price respectively the security in question. With the migration of the Frankfurt Stock Exchange trading to Xetra technology these were largely abolished.