what's the meaning of "bd" in "inaturalist19_bd_embeddings.pkl" file?

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This work means a lot to me, thank you for sharing this interesting work. I have come across some files named as xxxxx_bd_embeddings.pkl in data folders, and I'm curious about their meaning. Specifically, what does the abbreviation 'bd' stand for in these filenames? Upon reading the files, I found they contain dictionaries that appear to be measuring relationships between categories. Could you please explain the specific meaning of these values? Looking forward to your response.