3D modeling (also known as meshing) is the process of developing a mathematical representation of any three-dimensional surface of object (either inanimate or living) via specialized software. wikipedia.org

A level, map, area, or world in a video game is the total space available to the player during the course of completing a discrete objective. The term "level" can also refer to difficulty level, as in a degree of difficulty. wikipedia.org

Game design, a subset of game development, is the process of designing the content and rules of a game in the pre-production stage and design of gameplay, environment, storyline, and characters during production stage. wikipedia.org

Game development is the generally involved and lengthy process of creating a video game. Development is undertaken by a game developer, which may range from a single person to a large business. wikipedia.org