What is the meaning of "vnd" in MIME types?
vnd indicates vendor-specific MIME types, which means they are MIME types that were introduced by corporate bodies rather than e.g. an Internet consortium.
vnd = vendor.
See Wikipedia - Media type:
Types or subtypes that begin with
x-are nonstandard[2] (they are not registered with IANA). Subtypes that begin withvnd.are vendor-specific; subtypes in the personal or vanity tree begin withprs..[3]