A plaintext description of the various data types including the quality control fields and the file formats.

This resource can be downloaded or viewed using the link: ukb_genetic_data_description.txt

If you have wget available (typically on linux systems), then you can also obtain a copy using the command

 wget  -nd  biobank.ctsu.ox.ac.uk/ukb/ukb/docs/ukb_genetic_data_description.txt