Cloud masking
From AWF-Wiki
Sentinel-2 cloud masking
The exclusion of clouds and cloud shadow is an important processing step which is usually done in an early preprocessing stage. The Sentinel-2 products are annotated with Quality Indicators (QI_DATA).In the Level 2A product you may find a file in the folder QI_DATA with the extension _CLD_20m.jp2 which might be used for masking clouds.
