Demo

A demo (from "demonstration") is a short, free sample of a game. It is a type of promotional material that is meant to entice someone to follow and eventually purchase and/or promote a game because they played and enjoyed the sample. Often, it’s the prologue and/or first chapter of the visual novel - or even the full common route. Sometimes, it’s a short stand-alone story set in the same world that may or may not involve the same characters that are in the full game. It should ideally feature the same tone and at least some of the same features as the full game would. (The Stanley Parable is a good example of a branching story game that has an excellent stand-alone demo.) Visual Novel demos often run less than an hour of play time.

A vertical slice is a type of demo that shows a sample of the elements/features of a game. For example, if your VN offers text box dialogue, timed choices, and two different mini-games, your vertical slice would include at least a short scene with dialogue, one timed choice, and some time with each of the two mini-games. If you don’t have any sort of gameplay elements, but do have multiple characters to romantically pursue, you can also do a vertical slice using scenes with each of the dateable characters to give players a feel for their routes. (The demo for No Thank You! ^[VNDB] is an example.) The advantage of having a vertical slice demo is that you can "skip around" with your content and show features that aren’t available until later in the game. The disadvantage is that it can feel disjointed if not done well.