Overhead in computing refers to additional, indirect computation effort required for a specific task. This may include computation time, memory usage, bandwidth or other resources. In communication specifically, there is data transfer overhead, which refers to the various types of control and signalling data that is required for the payload to reach its destination.
Similarly, encoded audio has overhead data in addition to the audio signal. In the case of transport streams there is also overhead caused by padding. TS transport packages are 188 bytes, which is usually larger than the audio frame of most codecs. This means the rest of the package must be padded to fill out the 188 bytes. The exact amount of overhead can vary based on multiple factors, like the amount of additional data that is inserted (which may be very large in the case of overhead caused by processes like Forward Error Correction), the complexity of encoding and transport processes and the latency that the operator is willing to accept. In some transport protocols and methods, the packet size can also be adjusted, which is another way the overhead and latency can be affected.