Batch Field- MARA-SLED_BBD

Hi team,

I have found the field "SLED_BBD" in MARA table. In this field we have below values.

B- Expiration date

E- Shelf life expiration date.

Currently in my system for one material the value "B" has been set. What does it mean? Till now I understand that "expiration Date" & 'Shelf life expiration date" both are same. How this table field is getting updated in SAP while creating the material master?

thanks