Do "download" and "upload" only refer to networks?

I know what it means to download something from a website or upload a video to YouTube. But do the terms "download" and "upload" only apply when referring to one device transferring data to another remote device over the Internet (or LAN even)?

Say I was transferring a file to my USB flash drive or copying a file from one HDD to another HDD. Would this technically be considered downloading/uploading?

Yes, technically if could be considered downloading/uploading, but if you use it that way it may get confusing.

Downloading/uploading is generally used when you connect the computer to a distant source, for example a server on internet. If you use it for small devices, it's not as obvious which direction is up or down.

If you for example have a network storage unit in your network, it's not at all clear if it should be considered as a server or a storage device, and uploading would have completely different meaning depending on what definition you choose.

Dictionary.com defines download as

verb (used with object) Computers.

to transfer (software, data, character sets, etc.) from a distant to a nearby computer, from a larger to a smaller computer, or from a computer to a peripheral device.

So yes, copying a file from your computer to flash drive or external HDD is downloading, but copying it from one HDD inside your computer to another also inside your computer is not.

Note that, upload and download (usually) refer to exchange of information between a local system and a remote system. Also, in the context of the systems involved, the terms local and remote are independent of size, distance or the utility of the object. They may be close or far or even the same box (ex: two hard drives in the same system). The terms - upload and download - are therefore generic in nature.

A transfer from local system to remote system is called upload where as from remote to local system is called download.