The TDMS file (.tdms) format is designed to write and read measured data, while maintaining a hierarchical system of descriptive information. TDMS file contains two types of data: meta data and raw data. Meta data is descriptive data stored in objects or properties. Data arrays attached to channel objects are referred to as raw data.
See Also
The NI TDMS File Format (on NI web site)
TDMS File Format Internal Structure (on NI web site)