I'm not familiar with the specific meaning or context of "bdd-31". This could be:

1. A model number or part designation for a product or device

2. An abbreviation or code used in a particular field or organization

3. A typo or misspelling of something else

Without more context about where you encountered this term or what it might relate to, I can't provide a more specific answer. If you have any additional information about the context or source of this term, please share it and I'll do my best to help further.