To download a file, esp. an application, to a smartphone or other electronic device outside of the accepted or usual channels.
The app center says the eBay app isn't available yet for the new OS on my phone, so I had to sideload an earlier version from a Dropbox link I found.
de Eduardo Suave 6 septembre 2011
To upload or download information from the side of a PC, usually through a USB port.
I'm sideloading the music to my Zune
de Jerse47 1 mars 2009