Stand by time for the mobiles
Standby time is the time which is the officially quoted longest time a single battery lasts when the phone is not in active use but is connected to the GSM network all the time.
The standby time is highly dependent on the cellular network lik the distance to the closest GSM cell tower or the base station. If you use the phone while travelling , like in a moving vehicle, also affects the battery life.
Likewise the Talk Time is the officially quoted talk time , the longest a single battery will last when you are continuosly talking on the phone. This also just like the standby time is dependent on the cellular network and the distance from the GSM to the cell station. Moving fast while talking also affects the battery life.
Music Play back time is the longest time officially quoted by the manufacturer that a single battery charge will last if you are using the phone continuously for listening to music only. These numbers work usually when the handsets are set in flight mode that is all the transreceivers are off and the headphones are used instead of speakers.
Manufacturers measure the talk time, standby time and the music play back time, in very much controlled conditions and the quoted numbers are rarely reached in the real life. You can use those numbers while comparing the handsets, as a reference, but only of the same manufacturer as the calculations vary from manufacturrto manufacturer.
Some times the place in the specifications will be empty, as all the manufacturuers do not disclose the number of hours at the time of launching the product. Later, only when the product hit the market the standby time as well as talk time gets revealed.