To receive a data file on one's computer from another computer (which can be a file server, a bulletin board service, an Internet USENET group, or another individual's computer), typically via modem. The opposite, upload, means to send a data file from one's computer to another computer.
Similarly, laser printers and other output devices frequently download data (such as the file to be printed, and the fonts with which to print it) from the computer. (See Downloadable Font.)