Upload speed represents the time that it takes to send or transfer data from your device to the internet. For example, when you are video calling on skype or zoom, you are uploading information. Whether you are using a webcam or screen sharing, you will be uploading information through the internet for the other person to receive.
Most uploading happens when information is backed up to the cloud, through video calling, streaming, or sending large files. Just like download speed, your upload speed is also measured in Mbps or megabits per second.