A proxy is used to replace an element in the video sequence when exporting a file for some time during editing. It is often a version of an existing element of the video sequence, but with a low resolution or as a still image. Quite often, images from a storyboard are used as proxies. You can use a proxy https://soax.com/911-proxy-socks before the final version of the video sequence is available, or if there is a real video sequence element, to speed up previewing or rendering test movies. To use a proxy, you must have a file available.