A digital billboard is a large outdoor LED display carrying scheduled advertising, normally sold as rotating slots shared between advertisers rather than a single fixed poster.
The change from print is operational rather than visual. Creative can be swapped within hours instead of weeks, scheduled by time of day, and switched in response to weather or an event, which is what turned outdoor from a booked-in-advance medium into a reactive one.
The caveat is that outdoor hardware is a different engineering problem entirely. Brightness has to overcome direct sunlight and then dim automatically at night or it becomes a driving hazard, a regulated one in most jurisdictions. Weatherproofing, heating, cooling and lightning protection all apply, and the failure modes are expensive because access needs equipment.
Planning permission is the other reality: brightness limits, permitted animation, and whether motion is allowed at all vary by municipality and are frequently stricter near roads. Those constraints shape the creative, so they belong at the start of a campaign conversation rather than at the end.