Where does the term blob come from in a git context?

git man page

seems surprisingly devoid of an official definition, other than this (focus):

Object database contains objects of three main types: blobs, which store file data ; trees that point to blobs and other trees to create a directory hierarchy; and commits, each of which refers to one tree and a number of parent commits.

Reusing the term "object database" in the git documentation implies borrowing "blob" specifically from the DBMS.

In its article on Binary Large Objects, Wikipedia defines the term "collection of binary data stored as a single unit in a database management system" as follows:

Blobs were originally just amorphous chunks of data invented by Jim Starkey at DEC, who describes them as "what Cincinnati, Cleveland or whatever ate" from the 1958 Steve McQueen movie, referring to The Blob. Later, Terry McKeever, Apollo Marketing Specialist, felt that it should be an acronym and invented the basic Backronym big object. Then Informix invented an alternative backronym, the Binary Large Object.

So while this is not a definitive answer, the term "blob" has a common and well-defined use in computer science as an opaque string of binary data, and git sticks to that definition without elaborating on it.