What does 'data grain' mean?

In the context of data engineering and analysis, the term data grain refers to the level of granularity, or detail, at which data is stored and analyzed. In other words, data grain refers to the size and scope of the individual pieces of data that are collected and processed.

For example, a data set that is collected and analyzed at the level of individual transactions would have a fine grain, while a data set that is analyzed at the level of monthly totals would have a coarse grain. The appropriate data grain for a given analysis will depend on the specific questions being asked and the goals of the analysis.

Data grain is an important consideration in data engineering and analysis because it can impact the accuracy and usefulness of the data. Data sets with a fine grain of detail can provide more detailed and accurate insights, but may require more computational resources to process and analyze. On the other hand, data sets with a coarse grain of detail may be less accurate, but can be easier and faster to work with. Choosing the appropriate data grain is therefore an important part of designing and implementing a data analysis system.