When you make edits, apply filters, color corrections etc... those are applied to the video usually in a temporary fashion, so you can see what you are doing while you are editing. These changes are either held in RAM, or a temporary storage format. This is rendering - the process of applying those changes you make to the video. When you export the final video, the editor has to render , because it's applying the changes you specificed. But it also has to encode the video - usually applying some sort of compression to the export