From VNDev Wiki

Scope is the art of identifying and planning for a game project - and sticking to that plan. For a visual novel project, your scope for the game would include the number of main characters (ex: romanceable heroines), the number of routes/endings, a general estimate of how many hours of content there would be, and if there are gameplay elements, which elements to include.

During development, there is often the urge to add more to a project as you get excited about it - “We could add [this feature], and it would be so cool!” or “I really like this side character, let’s make them another romanceable character!” While the extra ideas can certainly add to the game, it also means more development time and usually also costs. It can make it easy to run out of budget, burn through enthusiasm from dev team members, or even go beyond the current skill levels of the dev team. If you have ideas for things beyond your original scope, it is recommended that you write the ideas down and add them only after you have completed the original project's plans.