A held run of bytes with no structure the system reads. A blob is content the store agrees not to understand.
Middle English blobbe/bleb, likely imitative of a soft rounded lump, cousin to 'blister' and 'bubble'; no fixed shape, only a shape's absence, is the word's oldest sense.
A held run of content the system agrees not to parse — matter kept, not read, a shape without an inside anyone has to understand.