Definition: It's a file in Linux or Unix environments with some specific configuration info, often used for logging purposes. 'Phys' might be referring to physical hardware (like a CPU). 'Header' typically refers to headers of files within it. Conf stands for Configuration File. So '.0100_phys_header.conf' is part of the filesystem and contains logging information related to a specific hardware or program, like a CPU. Detailed definition could include configuration settings for logging, file systems permissions etc.