1. transfer a file or program from a central computer to a smaller computer or to a computer at a remote location;
WordNet (r) 3.0 (2006):
v 1: transfer a file or program from a central computer to a
smaller computer or to a computer at a remote location
The Jargon File (version 4.4.7, 29 Dec 2003):
To transfer data or (esp.) code from a far-away system (especially a larger
host system) over a digital communications link to a nearby system
(especially a smaller client system. Oppose upload.
Historical use of these terms was at one time associated with transfers
from large timesharing machines to PCs or peripherals (download) and
vice-versa (upload). The modern usage relative to the speaker (rather than
as an indicator of the size and role of the machines) evolved as machine
categories lost most of their former functional importance.
The Free On-line Dictionary of Computing (30 December 2018):
To transfer data from one computer to another.
Downloading usually refers to transfer from a larger "host"
system (especially a server or mainframe) to a smaller
"client" system, especially a microcomputer or specialised
peripheral, and "upload" usually means from small to large.
Others hold that, technically, download means "receive" and
upload means "send", irrespective of the size of the systems
Note that in communications between ground and space,
space-to-earth transmission is always "down" and the reverse
"up", regardless of size. So far the in-space machines have
invariably been smaller; thus the upload/download distinction
has been reversed from its usual sense.