The format can mean two things: for camcorders, in particular, the format can refer to what type of hardware your camcorder uses for memory and, in all cameras, the format can also refer to the size of an image sensor. Most modern camcorders record to solid-state drives (SSDs), and/or have a slot for removable Secure Digital (SD) cards. Both offer a memory type fast enough to capture 4K video, while cameras that take SD cards allow for expandable storage. As for the camera's sensor, you’ll likely want one that lets you shoot in that memory-hungry 4K format. This will allow you to “punch in” and re-frame your shots in post-production without noticing any significant quality loss.