What does upload mean?

Upload is the transmission of data from your device to the Internet. The upload data rate does not feature prominently in marketing materials and is usually much lower than the download data rate. But it is important for a fast Internet access jointly with the download data rate, because communications on the Internet are always in both directions. The upload data rate is specially important if you want to send photos, use file sharing technologies or conduct video conferences.

Please note that, with the upload rate too, there is a difference between gross and net data rate.