A TDR (Transaction Detail Records) is a database record which summarizes a diameter transaction (one request / answer message pair and associated TTR events) and DSR metadata associated with it. Every TDR is associated with a dictionary, which describes its structure.
One TTR is usually represented with more than one TDR, i.e. every TTR is split by IDIH Mediation server during the TTR processing into multiple TDR records each having one request / answer pair.