To upload means to send a file from your device to a website or another computer. It is like handing a paper document to someone who is not in the same room. A photo, form, or document can be uploaded.
For example, a job application might ask you to upload a résumé saved on your computer. A website may let you choose the file from a folder, drag it into a marked area, or do both.
Before sending a file, check that it is the right one and that the site accepts its type and size. A clear upload button and a visible file name help people confirm what they are about to send.