download (v.) is the act of copying data from a remote server to your computer or device. Conceptually, servers on the internet, or in “the cloud“, are viewed as being “up there” somewhere. While “up there” is so exceptionally vague as to be meaningless, it does at least imply a difference in altitude: the device in front of you sits, conceptually, lower than remote servers or services on the internet. Thus data is copied “down” from those servers to your machine. Conversely, copying data from your computer or device to an internet server is considered an upload.
download (n.) a file that has been downloaded.